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Highlights and News at MBI
Earlier Highlights are found in the archive
8 August 2018: Slow, but efficient: Low-energy electron emission from intense laser cluster interactions
For the past 30 years intense laser cluster interactions have been seen primarily as a way to generate energetic ions and electrons. In surprising contrast with the hitherto prevailing paradigm, a team of researchers has now found that copious amounts of relatively slow electrons are also produced in intense laser cluster interactions. These low-energy electrons constitute a previously missing link in the understanding of the processes occurring when an intense laser pulse interacts with a nanoscale particle, a situation that is highly relevant for the in-situ imaging of biomolecules on ultrashort timescales. ...more
 
27 July 2018: Concepts for new switchable plasmonic nanodevices: a magneto-plasmonic nanoscale router and a high-contrast magneto-plasmonic disk modulator controlled by external magnetic fields
Plasmonic waveguides open the possibility to develop dramatically miniaturized optical devices and provide a promising route towards the next-generation of integrated nanophotonic circuits for information processing, optical computing and others. Key elements of nanophotonic circuits are switchable plasmonic routers and plasmonic modulators. Recently Dr. Joachim Herrmann (MBI) and his external collaborators developed new concepts for the realization of such nanodevices. They investigated the propagation of surface-plasmon-polaritons (SPP) in magneto-plasmonic waveguides. Based on the results of this study they proposed new variants of switchable magneto-plasmonic routers and magneto-plasmonic disk modulators for various nanophotonic functionalities. ...more
 
27 July 2018: Benjamin Fingerhut receives the ERC Starting Grant
Dr. Benjamin Fingerhut, junior group leader at the Max Born Institute (MBI), is recipient of the prestigious ERC Starting Grant 2018. The project addresses ultrafast biomolecular dynamics via a non-adiabatic theoretical approach. The award is granted by the European Research Council (ERC) to support excellent researchers at the beginning of their independent research careers. ...more
 
13 July 2018: What happens when we heat the atomic lattice of a magnet all of a sudden?
Magnets have fascinated humans for several thousand years and enabled the age of digital data storage. They occur in various flavors. Ferrimagnets form the largest class of magnets and consist of two types of atoms. Similar to a compass needle, each atom exhibits a little magnetic moment, also called spin, which arises from the rotation of the atom's electrons about their own axes. In a ferrimagnet, the magnetic moments point in opposite directions for the two types of atoms (see panel A). Thus, the total magnetization is the sum of all magnetic moments of type 1 (M1), blue arrows) and type 2 (M2), green arrows). Due to the opposite direction, the magnitude of the total magnetization is M1-M2. ...more
 
21 June 2018: "Dr. Federico Furch named 2018 OSA Ambassador"
In October of 2017 the Optical Society (OSA) announced the 2018 class of OSA Ambassadors. One member of this class is MBI researcher Dr. Federico Furch, who in the last few years has been responsible for the development of a state-of-the-art 100 kHz OPCPA laser system that is currently being implemented in attosecond experiments. ...more
 
14 June 2018: "Picture of atomic orbitals featured in NOVA/PBS documentary"
Pictures of atomic hydrogen orbitals measured by MBI researchers are featured in a new NOVA/PBS documentary (see link). In the video, it is explained how the two-dimensional wavefunction of a hydrogen atom can be visualized by recording a large number of ionized electrons, one at a time, on a 2-dimensional detector. The results were published in Physical Review Letters in 2013 (see Highlight link MBI website). and voted one of the Top 10 breakthroughs in Physics in 2013 (see Highlight link MBI website). ...more.
 
13 June 2018: Dr. Daniela Rupp will receive the Karl Scheel Prize 2018
The Physical Society of Berlin announced this year's Karl Scheel laureate. We congratulate Dr. Daniela Rupp, who will receive the award on June 22, 2018 at 5 p.m. the Magnus-Haus in Berlin Mitte. ...more.
 
31 May 2018: X-Ray Holography reveals Nano-Patchwork during Phase Transition in Vanadium Dioxide
In the prototypical material VO2, the role of electronic correlation in the phase transition between the insulating and metallic phase have long been debated. Combining spectroscopy and holography with x-rays, an international team of scientists has now observed how tiny patches of different phases evolve during the phase transition. ...more.
 
4 May 2018: Laser-driven electron recollision remembers molecular orbital structure
Scientists from the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin combined state-of-the-art experiments and numerical simulations to test a fundamental assumption underlying strong-field physics. Their results refine our understanding of strong-field processes such as high harmonic generation (HHG) and laser-induced electron diffraction (LIED). The results have been published in "Science Advances". ...more.
 
16 April 2018: Freeing electrons to better trap them
For the first time, researchers from UNIGE and MBI in Berlin have placed an electron in a dual state - neither freed nor bound - thus confirming a hypothesis from the 1970s. ...more.
 
16 April 2018: From insulator to conductor in a flash
A clever combination of novel technologies enables us to study promising materials for the electronics of tomorrow. Over the past decades, computers have become faster and faster and hard disks and storage chips have reached enormous capacities. But this trend cannot continue forever: we are already running up against physical limits that will prevent silicon-based computer technology from attaining any impressive speed gains from this point on. ...more.
 
12 April 2018: Wiggling atoms switch the electric polarization of crystals
Ferroelectric crystals display a macroscopic electric polarization, a superposition of many dipoles at the atomic scale which originate from spatially separated electrons and atomic nuclei. The macroscopic polarization is expected to change when the atoms are set in motion but the connection between polarization and atomic motions has remained unknown. A time-resolved x-ray experiment now elucidates that tiny atomic vibrations shift negative charges over a 1000 times larger distance between atoms and switch the macroscopic polarization on a time scale of a millionth of a millionth of a second....more.
 
9 April 2018: X-ray snapshots of reacting acids and bases - Erik T. J. Nibbering receives an ERC Advanced Grant for groundbreaking basic research
Dr. Erik T. J. Nibbering of the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin receives an Advanced Grant from the European Research Council (ERC). Goal with this prestigious award is to investigate and elucidate the elementary steps of aqueous proton transfer dynamics between acids and bases. The ERC Advanced Grant is endowed with 2.5 million euro and awarded to well-established top researchers in Europe pursuing scientifically excelling projects. ...more.
 
27 February 2018: A spinning top of light
Short, rotating pulses of light reveal a great deal about the inner structure of materials. An international team of physicists led by Prof. Misha Ivanov of the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) has now developed a new method for precisely characterising such extremely short light pulses. The research results have been published in Nature Communications. ...more.
 
19 February 2018: C'mon electrons, let's do the twist! Twisting electrons can tell right-handed and left-handed molecules apart.
Identifying right-handed and left-handed molecules is a crucial step for many applications in chemistry and pharmaceutics. An international research team (CELIA-CNRS/INRS/ Berlin Max Born Institute/SOLEIL) has now presented a new original and very sensitive method. The researchers use laser pulses of extremely short duration to excite electrons in molecules into twisting motion, the direction of which reveals the molecules' handedness. The research results appear in Nature Physics. ...more.
 
16 January 2018: Flexibility and arrangement - the interaction of ribonucleic acid and water
Ribonucleic acid (RNA) plays a key role in biochemical processes which occur at the cellular level in a water environment. Mechanisms and dynamics of the interaction between RNA and water were now revealed by vibrational spectroscopy on ultrashort time scales and analyzed by in-depth theory. ...more.
 
15 January 2018: Instant x-ray footprints
MBI scientists together with colleagues from Italy have established a way to detect the exact x-ray fluence footprint generated on a sample by a free electron laser pulse. ...more.
 
1 January 2018: Marc Vrakking named Editor-in-Chief of the Journal of Physics B
Prof. Marc Vrakking, director of Division A of the Max Born Institute, has been named Editor-in-Chief of the Journal of Physics B from January 1st 2018. In this capacity he succeeds Prof. Paul Corkum of the University of Ottawa, who served as Editor-in-Chief since 2011. ...more.
 

 
More detailed Information:

 


Slow, but efficient: Low-energy electron emission from intense laser cluster interactions

8 August 2018

For the past 30 years intense laser cluster interactions have been seen primarily as a way to generate energetic ions and electrons. In surprising contrast with the hitherto prevailing paradigm, a team of researchers has now found that copious amounts of relatively slow electrons are also produced in intense laser cluster interactions. These low-energy electrons constitute a previously missing link in the understanding of the processes occurring when an intense laser pulse interacts with a nanoscale particle, a situation that is highly relevant for the in-situ imaging of biomolecules on ultrashort timescales.

When a nanoscale particle is exposed to an intense laser pulse, it transforms into a nanoplasma that expands extremely fast, and several phenomena occur that are both fascinating and important for applications. Examples are the generation of energetic electrons, ions and neutral atoms, the efficient production of X-ray radiation as well as nuclear fusion. While these observations are comparably well understood, another observation, namely the generation of highly charged ions, has so far posed a riddle to researchers. The reason is that models predicted very efficient recombination of electrons and ions in the nanoplasma, thereby drastically reducing the charges of the ions.

A team of researchers from the Imperial College London, the University of Rostock, the Max Born Institute, the University of Heidelberg and ELI-ALPS have now helped to solve this riddle. Tiny clusters consisting of a few thousand atoms were exposed to ultrashort, intense laser pulses. The researchers found that the vast majority of the emitted electrons were very slow (see Fig. 1). Moreover, it turned out that these low-energy electrons were emitted with a delay compared to the energetic electrons.

Lead scientist Dr. Bernd Schütte, who performed the experiments at Imperial College in the framework of a research fellowship and who now works at the Max Born Institute, says: "Many factors including the Earth's magnetic field influence the movement of slow electrons, making their detection very difficult and explaining why they have not been observed earlier. Our observations were independent from the specific cluster and laser parameters used, and they help us to understand the complex processes evolving on the nanoscale."

In order to understand the experimental observations, researchers around Professor Thomas Fennel from the University of Rostock and the Max Born Institute simulated the interaction of the intense laser pulse with the cluster. "Our atomistic simulations showed that the slow electrons result from a two-step process, where the second step relies on a final kick that has so far escaped the researchers' attention", explains Fennel. First, the intense laser pulse detaches electrons from individual atoms. These electrons remain trapped in the cluster as they are strongly attracted by the ions. When this attraction diminishes as the particles move farther away from each other during cluster expansion, the scene is set for the important second step. Therein, weakly bound electrons collide with a highly excited ion and thus get a final kick that allows them to escape from the cluster. As such correlated processes are quite difficult to model, the computing resources from the North-German Supercomputing Alliance (HLRN) were essential to solve the puzzle.

The researchers found the emission of slow electrons to be a very efficient process, enabling a large number of slow electrons to escape from the cluster. As a consequence, it becomes much harder for highly charged ions to find partner electrons that they can recombine with, and many of them indeed remain in high charge states. The discovery of the so-called low-energy electron structure can thus help to explain the observation of highly charged ions from intense laser cluster interactions. These findings might be important as low-energy electrons are implicated as playing a major role in radiation damage of biomolecules - of which the clusters are a model.

Senior author Professor Jon Marangos, from the Department of Physics at Imperial, says: "Since the mid-1990's we have worked on the energetic emission of particles (electrons and highly charged ions) from laser-irradiated atomic clusters. What is surprising is that until now the much lower energy delayed electron emission has been overlooked. It turns out that this is a very strong feature, accounting for the majority of emitted electrons. As such, it may play a big role when condensed matter or large molecules of any kind interact with a high intensity laser pulse."

3d Deutsch
Fig. 1 (click to enlarge)

Fig. 1: The electron kinetic energy spectrum from Ar clusters interacting with intense laser pulses is dominated by a low-energy structure (orange area). The inset shows the same spectrum on a logarithmic scale, indicating an exponential behavior both for the slow electron emission (red curve) and for the fast electron emission (green curve).

Phase Image
Fig. 2 (click to enlarge)
Fig. 2: Atomistic simulation of the laser-induced cluster explosion.

Original publication:
Bernd Schütte, Christian Peltz, Dane R. Austin, Christian Strüber, Peng Ye, Arnaud Rouzée, Marc J. J. Vrakking, Nikolay Golubev, Alexander I. Kuleff, Thomas Fennel and Jon P. Marangos
"Low-energy electron emission in the strong-field ionization of rare gas clusters"
Physical Review Letters 0031-9007/18/121(6)/063202(6)/ DOI:10.1103/PhysRevLett.121.063202

Further information:
Dr. Bernd Schütte, Tel.: 030 6392 1295
Prof. Dr. Thomas Fennel , Tel.: 030 6392 1245

 
     
 


Concepts for new switchable plasmonic nanodevices: a magneto-plasmonic nanoscale router and a high-contrast magneto-plasmonic disk modulator controlled by external magnetic fields

2nd August 2018

Plasmonic waveguides open the possibility to develop dramatically miniaturized optical devices and provide a promising route towards the next-generation of integrated nanophotonic circuits for information processing, optical computing and others. Key elements of nanophotonic circuits are switchable plasmonic routers and plasmonic modulators. Recently Dr. Joachim Herrmann (MBI) and his external collaborators developed new concepts for the realization of such nanodevices. They investigated the propagation of surface-plasmon-polaritons (SPP) in magneto-plasmonic waveguides. Based on the results of this study they proposed new variants of switchable magneto-plasmonic routers and magneto-plasmonic disk modulators for various nanophotonic functionalities.

In a waveguide based on a metal film with a thickness exceeding the Skin depth and surrounded by a ferromagnetic dielectric an external magnetic field in the transverse direction can induce a significant spatial asymmetry of mode distribution of surface-plasmon-polaritons (SPP). Superposition of the odd and the even asymmetric modes over a certain distance leads to a concentration of the energy on one interface which is switched to the other interface by magnetic field reversal. The requested magnitude of magnetization is exponentially reduced with the increase of the metal film thickness. Based on this phenomenon, the group proposed a new type of waveguide-integrated magnetically controlled switchable plasmonic routers. A configuration of such nanodevice is shown in Fig. 1 consisting of a T-shaped metallic waveguide surrounded by a ferromagnetic dielectric under an external magnetic field inducing a magnetization M. In Fig. 2 numerical results for the plasmon propagation by solving the Maxwell equation show channel switching by the magnetic field reversal with a 99%-high contrast within the optical bandwidth of tens of THz [1]. Here g is the gyration g=χM, χ is the magneto-optical susceptibility and g0 is a characteristic gyration requested to induce a significant mode asymmetry. Magnetic field reversal by integrated electronic circuits can be realized with a repetition rate in the GHz region. Note that up to now there exist only few papers reporting the realization of switchable plasmonic routers based on branched silver nanowires controlled by the polarization of the input light.

In a second paper [2] the group proposed and studied a novel type of ultra-small plasmonic modulator based on a metal-isolator-metal waveguide and a side-coupled magneto-optical disk controlled by an external magnetic field (see Fig.3). The wavenumber change and the transmission of surface-plasmon-polaritons (SPPs) can be tuned by altering the magnetic field and reversible on/off switching of the running SPP modes by a reversal of the direction of the external magnetic field is demonstrated. Resonant enhancement of the magneto-plasmonic modulation by more than 200 times leads to a modulation contrast ratio more than 90% keeping a moderate insertion loss within an optical bandwidth of hundreds of GHz. Numerical simulations by the solution of Maxwell's equations confirm the predictions by the derived analytical formulas of a high-contrast magneto-plasmonic modulation. Fig. 4 shows the distribution of the magnetic field components of the SPPs at a gyration g=0.03 and g=-0.03, respectively. As seen by changing the direction of the external magnetic field, the transmission of the SPPs is switched from an off to an on state via the changed interference pattern in the waveguide.

PM_Fig1
Abb. 1 (click to enlarge)

Fig 1: Configuration of a switchable plasmonic router consisting of a T-shaped metallic waveguide surrounded by a ferromagnetic dielectric material and under the action of an external magnetic field.

PM_Fig2
Abb. 2 (click to enlarge)
Fig 2: Numerical results for the distribution of the plasmon intensity demonstrating channel switching.The reversal of the direction of the external magnetic field leads to a switching of the SPP propagation from channel 1 in (a) to channel 2 in (b). The metal waveguide is made from gold and the surrounding ferromagnetic dielectric from Bi-substituted iron garnet (BIG).
PM_Fig3
Abb. 3 (click to enlarge)
Fig 3: Scheme of the magnetoplasmonic disk resonator side-coupled to a metal-insulator-metal waveguied and controlled by an external magnetic field.
PM_Fig3
Abb. 4 (click to enlarge)
Fig 4: Magnetic field distribution of the SPPs in a metal waveguide side-coupled to a disk resonator at the wavelength of 748nm. By changing the direction of the magnetic field the transmission of SPPs is switched from an off state (fig 4a) with g=-0.03 to an on state (Fig 4b) with g=0.03.The metal waveguide is made from silver and the ferromagnetic dielectric from Bi-substituted iron garnet (BIG).

Original publication:
Kum-Song Ho, Song-Jin Im, Ji-Song Pae, Chol-Song Ri, Yong-Ha Han and Joachim Herrmann
"Switchable plasmonic routers controlled by external magnetic fields by using magneto-plasmonic waveguides"

[1]Scientific Reports (2018) 8:10584 /DOI:10.1038/s41598.018.28567.8

Ji-Song Pae, Song-Jin IM, Kum-Song Ho, Chol-Song Ri, Sok-Bong Ro and Joachim Herrmann
"Ultracompact high-contrast magneto-optical disk resonator side-coupled to a plasmonic waveguide and switchable by an external magnetic field".

[2] Phys. Rev. B 98, 041406 (R) (2018).

Further information:
Dr. Joachim Herrmann, Tel.: 030 6392 1278

 
     
 


Benjamin Fingerhut receives the ERC Starting Grant


27 July 2018

Dr. Benjamin Fingerhut, junior group leader at the Max Born Institute (MBI), is recipient of the prestigious ERC Starting Grant 2018. The project addresses ultrafast biomolecular dynamics via a non-adiabatic theoretical approach. The award is granted by the European Research Council (ERC) to support excellent researchers at the beginning of their independent research careers.

As of today the European Research Council (ERC) has announced the awardees of its Starting Grants. In the highly competitive selection procedure, the research proposal of Benjamin Fingerhut has been selected for funding. ERC Starting Grants are designed to support excellent early career researchers in establishing their own independent research programme. ERC Starting Grants are awarded to researchers up to 7 years after their PhD to conduct a research programme at a European university or research institute. The grants are awarded under the "excellent science" pillar of Horizon 2020, the EU's research and innovation programme with a funding of up to Euro 1.5 million for a maximum of 5 years.

The successful project is devoted to the fundamental understanding of ultrafast biomolecular vibrational dynamics in the mid-IR/THz spectral region where biologically highly relevant dynamics occur. The innovative non-adiabatic approach addresses fundamental problems, such as proton transfer, vibrational lifetimes and the dissipation of excess energy. The project aims to elucidate ultrafast biomolecular vibrational dynamics in dipolar liquids, within nanoconfined environments and in the vicinity of biological interfaces. As such the non-adiabatic approach to biomolecular vibrational dynamics facilitates insight into transmembrane proton translocation mechanisms which is highly relevant as microscopic foundation of cell respiration.

Dr. Benjamin Fingerhut has joined the MBI in 2014. He is currently funded by an Emmy Noether Early Career Grant of the German Research Foundation (DFG) and has established the Biomolecular Dynamics Junior Research Group at the MBI. The group pursues close collaboration with experimental research conducted at MBI which applies the most advanced methods of femtosecond nonlinear vibrational spectroscopy for mapping the relevant interactions of biomolecular processes. The group's research involves the development of state-of-the-art spectroscopic simulation techniques and their application to the real-time determination of ultrafast structural dynamics of molecular and biomolecular systems. The group combines analytical and computational approaches for novel simulation protocols suited to investigate complex non-adiabatic dynamics.

Further information on Dr. Benjamin Fingerhut can be found at http://staff.mbi-berlin.de/fingerhu/and on ERC Grants https://erc.europa.eu/.

Contact:
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI)
Theory Department T4: Biomolecular Dynamics
Dr. Benjamin P. Fingerhut
Tel. 030 / 6392-1404


 
     
 


What happens when we heat the atomic lattice of a magnet all of a sudden?

13 July 2018

Magnets have fascinated humans for several thousand years and enabled the age of digital data storage. They occur in various flavors. Ferrimagnets form the largest class of magnets and consist of two types of atoms. Similar to a compass needle, each atom exhibits a little magnetic moment, also called spin, which arises from the rotation of the atom's electrons about their own axes. In a ferrimagnet, the magnetic moments point in opposite directions for the two types of atoms (see panel A). Thus, the total magnetization is the sum of all magnetic moments of type 1 (M1), blue arrows) and type 2 (M2), green arrows). Due to the opposite direction, the magnitude of the total magnetization is M1-M2.

When an insulating ferrimagnet is heated, the heat is first deposited in the atomic lattice which causes the atoms to move randomly around their cold positions. Finally, part of the heat also causes random rotation (precession) of the spins around their cold direction. Thus, magnetic order gets lost; the total magnetization (M1-M2) decreases and eventually vanishes if the temperature of the ferrimagnet exceeds a critical temperature, the so-called Curie temperature. Although this process is of fundamental importance, its dynamics are not well understood. Even for the ferrimagnet yttrium iron garnet (YIG), one of the most intensely researched ferrimagnets, it is unknown how long it takes until the heated atomic lattice and the cold magnetic spins reach equilibrium with each other. Previous estimates of this time scale differ from each other by a factor of up to one million.

A team of scientists from Berlin (Collaborative Research Center / Transregio 227 Ultrafast Spin Dynamics, Fritz Haber Institute and Max Born Institute), Dresden (Helmholtz Center), Uppsala (Sweden), St. Petersburg (Russia), and Sendai (Japan) have now revealed the elementary steps of this process. "To instantaneously and exclusively heat up the atomic lattice of a YIG film, we use a very specific and novel kind of stimulus: ultrashort bursts of laser light at terahertz frequencies. With a subsequently arriving visible laser pulse, we can then step-by-step trace the evolution of the initially cold magnetic spins. Essentially, we record a stop-motion movie of how the magnetization evolves." says Sebastian Maehrlein, who conducted the experiments. His colleague Ilie Radu from summarizes: "Our observations are striking. We found that sudden heating of the atomic lattice reduces the magnetic order of the ferrimagnet on two distinct time scales: an incredibly fast scale of only 1 ps and a 100,000 times slower scale of 100 ns."

These two time scales can be understood in analogy to water in a closed pot that is put into a hot oven. The hot air of the oven corresponds to the hot atomic lattice whereas the magnetic spins correspond to the water inside the pot (see panel A). Once the atomic lattice is heated by the terahertz laser burst, the enhanced random oscillations of the atoms lead to a transfer of magnetic order from spin type 1 to spin type 2. Therefore, both the magnetic moments M1 (blue arrows in panel B) and M2 (green arrows) are reduced by exactly the same amount (red arrows). This process evolves on the fast time scale, and the atomic spins are forced to heat up while leaving the total magnetization M1-M2 unchanged, just like water in a closed pot that has to keep its volume.

We know, however, that a heated ferrimagnet not only aims at reducing M1 and M2, but also its total magnetization M1-M2. To do so, part of the spin must be released to the atomic lattice. This situation is again completely analogous to the hot water in a closed pot: the pressure inside the pot increases but is slowly released to the outside through little leaks in the lid (see panel C). This leakage of angular momentum to the atomic lattice is exactly what happens in the ferrimagnet through weak couplings between spins and lattice.

"We now have a clear picture of how the hot atomic lattice and the cold magnetic spins of a ferrimagnetic insulator equilibrate with each other." says Ilie Radu. The international team of researchers discovered that energy transfer proceeds very quickly and leads to a novel state of matter in which the spins are hot but have not yet reduced their total magnetic moment. This "spin overpressure" is released through much slower processes that permit leakage of angular momentum to the lattice. "Our results are also relevant for applications in data storage." Sebastian Maehrlein adds. ÔÇťThe reason is simple. Whenever we want to switch the value of a bit between 0 to 1 in a magnetic storage medium, angular momentum and energy have to finally be transferred between atomic lattice and spins."

3d Deutsch
Fig. 1 (click to enlarge)

Fig. 1: Heating a magnet without changing its magnetization. (A) A ferrimagnet consists of two spin sorts of opposite orientation (green and blue arrows). In the experiment, the atomic lattice of the ferrimagnet is heated by an extremely short terahertz laser pulse. This situation is analogous to heating the air (=atomic lattice) inside an oven that contains a pot with water (=spins). (B) Heat is transferred into the spin system and decreases the magnetization of each spin type by exactly the same amount. This process arises because spin is transferred from the blue to the green spin sort. Thus, the magnet is heated without changing its total magnetization! In the pot analogy, heat is transferred from the air outside the pot to the water inside. While the amount of water in the pot has not changed, an overpressure has built up. (C) Finally, the hot spins release their overpressure to the atomic lattice, thereby reducing the total magnetization. In the analogy, water overpressure is released through little leaks in the pot lid. (Source: FHI)


Original publication:
S. F. Maehrlein, I. Radu, P. Maldonado, A. Paarmann, M. Gensch, A. M. Kalashnikova, R. V. Pisarev, M. Wolf, P. M. Oppeneer, J. Barker, T. Kampfrath
Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation.

Sci. Adv. 4, eaar5164 (2018).

Futher Information:
Dr. Ilie Radu, Tel.: 030 6392 1357

 
     
 


Dr. Federico Furch named 2018 OSA Ambassador

21 June 2018

In October of 2017 the Optical Society (OSA) announced the 2018 class of OSA Ambassadors. One member of this class is MBI researcher Dr. Federico Furch, who in the last few years has been responsible for the development of a state-of-the-art 100 kHz OPCPA laser system that is currently being implemented in attosecond experiments. (see Highlight link MBI website).

Furch Osa Ambassador (click to enlarge) Source: MBI

"Some of the OSA Ambassadors at the OSA headquarters in Washington DC, during the Spring leadership meeting. Dr. Federico Furch, second to the left"

As stated in the press release by Chad Stark, president of the OSA Foundation, "OSA Ambassadors are dedicated to supporting OSA's student chapters and local sections, student members and other early career professionals. By sharing their experiences and knowledge, Ambassadors become an important component of OSA's professional development programs and outreach."

All OSA Ambassadors attended the spring leadership meeting at the OSA headquarters in Washington DC, in April of 2018. Moreover, they will attend the student leadership meeting taking place in September, also in Washington. As part of the Ambassadors program Federico has already engaged in activities with students chapters in Berlin, Potsdam, Argentina and Chile. He visited the Ukraine in early June, will visit Argentina and Chile in August, and India in October. During each of these activities he represents not only the OSA, but naturally, the Max Born Institute as well.

Recently, in June, Federico supported the BerlinOptik student chapter and 2016 OSA Ambassador Dr. Aline Dinkelaker in the organization of the career development event "working in Photonics in Berlin," where the Max Born Institute was represented by Prof. Marc Vrakking. He also organized a networking and information event for MBI students, where they were able to interact with the members of the BerlinOptik student chapter and the student chapter at Potsdam University.

Federico's OSA-related activities will continue throughout the year and MBI students that want to know more about OSA and the activities of student chapters are encouraged to contact him.

For more information please consult:
"The Optical Society Announces 2018 Ambassadors"
"2018 Ambassadors"

Contact:

Dr. Federico Furch, Tel.: 030 6392 1277

 

 

 
     
 


"Picture of atomic orbitals featured in NOVA/PBS documentary"

14 June 2018

Pictures of atomic hydrogen orbitals measured by MBI researchers are featured in a new NOVA/PBS documentary (see link). In the video, it is explained how the two-dimensional wavefunction of a hydrogen atom can be visualized by recording a large number of ionized electrons, one at a time, on a 2-dimensional detector. The results were published in Physical Review Letters in 2013 (see Highlight link MBI website). and voted one of the Top 10 breakthroughs in Physics in 2013 (see Highlight link MBI website).

Link to video on Youtube: "What does an atom actually look like"
Source: Greg Kestin PhD, Digital Producer, NOVA/ PBS, Preceptor, Harvard University Physics Department

Link to Original Publication Physical Review Letters 2013: "Hydrogen Atoms under Magnification: Direct Observation of the Nodal Structure of Stark States"

Link to Press Release: "Hydrogen atoms under the magnifying glass: Direct Observation of the Nodal Structures of Electronic States of the Hydrogen Atom"

Link to Top10 breakthrough in Physics 2013: "Internationales Forscherteam des MBI & AMOLF in den "top 10 breakthroughs" in "physicsworld.com" 2013"

Contact:

Prof. Marc J. Vrakking, Tel.: 030 6392 1200

 

 

 
     
 


Dr. Daniela Rupp will receive the Karl Scheel Prize 2018

13 June 2018

The Physical Society of Berlin announced this year's Karl Scheel laureate. We congratulate Dr. Daniela Rupp, who will receive the award on June 22, 2018 at 5 p.m. the Magnus-Haus in Berlin Mitte.

SmirnovaPanel

Dr. Daniela Rupp is junior research group leader at the Max Born Institute, Berlin

For more information please consult: "Der Karl-Scheel-Preis der Physikalischen Gesellschaft zu Berlin"

Contact:

Dr. Daniela Rupp, Tel.: 030 6392 1280

 

 

 
     
 


X-Ray Holography reveals Nano-Patchwork during Phase Transition in Vanadium Dioxide

31 May 2018

In the prototypical material VO2, the role of electronic correlation in the phase transition between the insulating and metallic phase have long been debated. Combining spectroscopy and holography with x-rays, an international team of scientists has now observed how tiny patches of different phases evolve during the phase transition.

The interplay of the positions of the atomic nuclei and the spatial distribution and energies of the electrons providing the "glue" holding them together defines the properties of the materials that make up our world. Of particular interest to researchers is to understand the mechanisms at play in phase transitions. For example, vanadium dioxide (VO2) is insulating at low temperatures and becomes metallic above about 65°C. The change in the electronic structure (insulating vs. metallic) is accompanied by a change of the crystal structure from a monoclinic (M1) structure to a rutile (R) structure, with a minute change of atomic positions (See Fig.1). The driving forces for this phase transition have been a matter of long standing debate, specifically the role of electronic correlation in thin VO2 films, where it had been reported that the material turns metallic at slightly lower temperatures even before the atoms rearrange to the R-structure.

A team of scientists from the Max Born Institute and the Technical University in Berlin, the ICFO and ALBA in Spain as well as the Vanderbildt University in the USA have now investigated this phase transition in thin VO2 films using x-ray spectro-holography. This technique allows to probe the electronic structure with 40 nm spatial resolution and can thus shed light on the role of inhomogeneity in the mechanism of the phase transition on the nanoscale. In the journal Nano Letters the researchers report that defects in the VO2 film can locally change the pathway of the phase transition. The picture that emerges from temperature series of spectro-holographic images through the phase transition as shown in Fig. 2 is the following:

When raising the temperature, growth of metallic regions in R-structure start from nanoscale defects. At these defects, "misplaced atoms" generate a strain in their neighborhood that reduce the energy required for the M1 to R transition to occur. In turn, the volume mismatch between these two phases locally generates a new strain field, triggering the growth of domains in yet another, different monoclinic phase called M2 in adjacent regions. This effect hence leads to a coexistence of different phases of the material on the nanometer length scale, as seen e.g. as a stripe pattern at 335°K (62°C) in Fig. 2. At higher temperature, these still insulating M2 phases will ultimately also transform into the metallic R phase - just like some of the M1 phase patches will do directly. The pathway for the insulator to metal phase transition is thus not homogeneous throughout the thin VO2 film, but varies spatially. Researchers have been blind to the inhomogeneity on this small lengthscale in the past and may thus have come to wrong conclusions by averaging over these regions in their experiments. In particular, in this new work no evidence for reduced electronic correlations or a new monoclinic yet metallic phase below the phase transition temperature is seen, as has been discussed in the past. The results highlight the importance of combining spatial and spectroscopic resolution and will serve as the basis to study the dynamics of laser-driven phase transitions in materials with electronic correlation.

3d Deutsch
Fig. 1 (click to enlarge)

Fig. 1: Crystal structures for the insulating monoclinic phases M1 and M2 as well as for the metallic R rutile structure. Minute changes in atomic positions have a large effect on the material properties. Vanadium atoms are shown in orange, oxygen atoms in blue. Connecting lines are meant as guide to the eye.

Phase Image
Fig. 2 (click to enlarge)
Fig. 2: Images of the phase separation occurring when heating a 75 nm thin VO2 film. The images were acquired via x-ray spectro-holography and are displayed in false color to indicate the different regions: red = defect region, black = M1 phase, blue = M2 phase, green = R phase. Note that some sample regions transition directly from M1 to R (e.g. cross marker) while others transition via the intermediate M2 phase (e.g. diamond marker).

Original publication:
Luciana Vidas, Christian M. Günther, Timothy A. Miller, Bastian Pfau, Daniel Perez-Salinas, Elías Martínez, Michael Schneider, Erik Gührs, Pierluigi Gargiani, Manuel Valvidares, Robert E. Marvel, Kent A. Hallman, Richard F. Haglund, Jr., Stefan Eisebitt, and Simon Wall
Imaging Nanometer Phase Coexistence at Defects During the Insulator-Metal Phase Transformation in VO2 Thin Films by Resonant Soft X-ray Holography

Nano Letters, Article ASAP, DOI: 10.1021/acs.nanolett.8b00458.

Further information:
Prof. Dr. Stefan Eisebitt, Tel.: 030 6392 1300
Dr. Bastian Pfau , Tel.: 030 6392 1343

 
     
 


Laser-driven electron recollision remembers molecular orbital structure


4 May 2018

Scientists from the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin combined state-of-the-art experiments and numerical simulations to test a fundamental assumption underlying strong-field physics. Their results refine our understanding of strong-field processes such as high harmonic generation (HHG) and laser-induced electron diffraction (LIED). The results have been published in "Science Advances".

Strong infrared laser pulses can extract an electron from a molecule (ionization), accelerate it away into free space, then turn it around (propagation), and finally collide it with the molecule (recollision). This is the widely used three-step model of strong-field physics. In the recollision step, the electron may, for example, recombine with the parent ion, giving rise to high harmonic generation, or scatter elastically, giving rise to laser-induced electron diffraction.

One of the commonly used assumptions underlying attosecond physics is that, in the propagation step, the initial structure of the ionized electron is "washed out", thus losing the information on the originating orbital. So far, this assumption was not experimentally verified in molecular systems.

A combined experimental and theoretical study at the Max Born Institute Berlin investigated the strong-field driven electron recollision dynamics in the 1,3-trans-butadiene molecule. In this molecule, the interaction with the strong laser field leads mainly to the ionization of two outermost electrons exhibiting quite different densities, see Figure 1. The state-of-the-art experiments and simulations then allowed the scientists to measure and calculate the high-angle rescattering probability for each electron separately. These probabilities turned out to be quite different both in the measurements and in the simulations. These observations clearly demonstrate that the returning electrons do retain structural information on their initial molecular orbital.

Schell Electron
Fig. 1 (click to enlarge)

Fig. 1: Continuum electronic wavepackets for strong-field ionization channel 1 and 2 in 1,3-trans-butadiene shortly after ionization. | Fig. MBI | Abb. MBI

Original publication:
"Molecular orbital imprint in laser-driven electron recollision"
Felix Schell, Timm Bredtmann, Claus Peter Schulz, Serguei Patchkovskii, Marc J. J. Vrakking and Jochen Mikosch
Science Advances, Vol. 4, no. 5, eaap8148 (2018), DOI: 10.1126/sciadv.aap8148

Contact:
Dr. Jochen Mikosch, Tel. 030 / 6392 1295
Dr. Timm Bredtmann, Tel. 030 / 6392 1251

 
     
 


Freeing electrons to better trap them


16 April 2018

For the first time, researchers from UNIGE and MBI in Berlin have placed an electron in a dual state - neither freed nor bound - thus confirming a hypothesis from the 1970s.
Atoms are composed of electrons moving around a central nucleus they are bound to. The electrons can also be torn away, overcoming the confining force of their nucleus, using the powerful electric field of a laser. Half a century ago, the theorist Walter Henneberger wondered if it was possible to free an electron from its atom with the laser field, but still make it stay around the nucleus. Many scientists considered this hypothesis to be impossible. However, it was recently successfully confirmed by physicists from the University of Geneva (UNIGE), Switzerland, and the Max Born Institute (MBI) in Berlin, Germany. For the first time, they managed to control the shape of the laser pulse to keep an electron both free and bound to its nucleus, and were at the same time able to regulate the electronic structure of this atom dressed by the laser. What's more, they also made these unusual states amplify laser light. They also identified a no-go area. In this area nicknamed "Death Valley", physicists lose all their power over the electron. These results shatter the usual concepts related to the ionisation of matter. The results have been published in the journal Nature Physics.

Since the 1980s, many experiments have tried to confirm the hypothesis advanced by the theorist Walter Henneberger: an electron can be placed in a dual state that is neither free nor bound. Trapped in the laser, the electron would be forced to pass back and forth in front of its nucleus, and would thus be exposed to the electric field of both the laser and the nucleus. This dual state would make it possible to control the motion of the electrons exposed to the electric field of both the nucleus and the laser, and would let the physicists to create atoms with "new", tunable by light, electronic structure. But is this really possible?

Leveraging the natural oscillations of the electron
The more intense a laser is, the easier should it be to ionise the atom - in other words, to tear the electrons away from the attracting electric field of their nucleus and free them into space. "But once the atom is ionised, the electrons don't just leave their atom like a train leaves a station, they still feel the electric field of the laser", explains Jean-Pierre Wolf, a professor at the applied physics department of the UNIGE Faculty of Sciences. "We thus wanted to know if, after the electrons are freed from their atoms, it is still possible to trap them in the laser and force them to stay near the nucleus, as the hypothesis of Walter Henneberger suggests", he adds.

The only way to do this is to find the right shape for the laser pulse to be applied, to impose oscillations on the electron that are exactly identical, so that its energy and state remain stable. "The electron does naturally oscillate in the field of the laser, but if the laser intensity changes these oscillations also change, and this forces the electron to constantly change its energy level and thus its state, even leaving the atom. This is what makes seeing such unusual states so difficult", adds Misha Ivanov, a professor at the theoretical department of MBI in Berlin.

Modulating laser intensity to avoid Death Valley
The physicists tested different laser intensities so that the electron freed from the atom would have steady oscillations. They made a surprising discovery. "Contrary to natural expectations that suggest that the more intense a laser is, the easier it frees the electron, we discovered that there is a limit to the intensity, at which we can no longer ionise the atom", observes Misha Ivanov. "Beyond this threshold, we can control the electron again". The researchers dubbed this limit "Death Valley", following the suggestion of Professor Joe Eberly from the University of Rochester.

Confirming an old hypothesis to revolutionise physics theory
By placing the electron in a dual state which is neither free nor bound, the researchers found a way to manipulate these oscillations as they like. This enables them to directly work on the electronic structure of the atom. After several adjustments, for the first time, physicists from UNIGE and MBI were able to free the electron from its nucleus, and then trap it in the electric field of the laser, as Walter Henneberger suggested. "By applying an intensity of 100 trillion watts per cm2, we were able to go beyond the Death Valley threshold and trap the electron near its parent atom in a cycle of regular oscillations within the electric field of the laser", Jean-Pierre Wolf says enthusiastically. As a comparison, the intensity of the sun on the earth is approximately 100 watts per m2.

"This gives us the option of creating new atoms dressed by the field of the laser, with new electron energy levels", explains Jean-Pierre Wolf. "We previously thought that this dual state was impossible to create, and we've just proved the contrary. Moreover, we discovered that electrons placed in such states can amplify light. This will play a fundamental role in the theories and predictions on the propagation of intense lasers in gases, such as air", he concludes.

NautePhotonics
Abb. (click to enlarge)

Schematic illustration of the Kramers Henneberger potential formed by a mixture of the atomic potential and a strong laser field. Source: UNIGE - Xavier Ravinet

Original publication:
"Amplification of intense light fields by nearly free electrons"
Mary Matthews, Felipe Morales, Alexander Patas, Albrecht Lindinger, Julien Gateau, Nicolas Berti, Sylvain Hermelin, Jérôme Kasparian, Maria Richter, Timm Bredtmann, Olga Smirnova, Jean-Pierre Wolf and Misha Ivanov
Nature Physics (2018), DOI:10.1038/s41567-018-0105-0

Contact:
Prof. Dr. Misha Ivanov, Tel. 030 / 6392 1210

 
     
 


From insulator to conductor in a flash

16 April 2018

A clever combination of novel technologies enables us to study promising materials for the electronics of tomorrow. Over the past decades, computers have become faster and faster and hard disks and storage chips have reached enormous capacities. But this trend cannot continue forever: we are already running up against physical limits that will prevent silicon-based computer technology from attaining any impressive speed gains from this point on. Researchers are particularly optimistic that the next era of technological advancements will start with the development of novel information-processing materials and technologies that combine electrical circuits with optical ones. Using short laser pulses, a research team led by Misha Ivanov of the Max Born Institute in Berlin together with scientists from the Russian Quantum Center in Moscow have now shed light on the extremely rapid processes taking place within these novel materials. Their results have appeared in the prestigious journal "Nature Photonics".

Of particular interest for modern material research in solid state physics are "strongly correlated systems", so called for the strong interactions between the electrons in these materials. Magnets are a good example of this: the electrons in magnets align themselves in a preferred direction of spin inside the material, and it is this that produces the magnetic field. But there are other, entirely different structural orders that deserve attention. In so-called Mott insulators for example, a class of materials now being intensively researched, the electrons ought to flow freely and the materials should therefore be able to conduct electricity as well as metals. But the mutual interaction between electrons in these strongly correlated materials impedes their flow and so the materials behave as insulators instead.

By disrupting this order with a strong laser pulse, the physical properties can be made to change dramatically. This can be likened to a phase transition from solid to liquid: as ice melts, for example, rigid ice crystals transform into free-flowing water molecules. Very similarly, the electrons in a strongly correlated material become free to flow when an external laser pulse forces a phase transition in their structural order. Such phase transitions should allow us to develop entirely new switching elements for next-generation electronics that are faster and potentially more energy efficient than present-day transistors. In theory, computers could be made around a thousand times faster by "turbo-charging" their electrical components with light pulses.

The problem with studying these phase transitions is that they are extremely fast and it is therefore very difficult to "catch them in the act". So far, scientists have had to content themselves with characterising the state of a material before and after a phase transition of this kind. Researchers Rui E. F. Silva, Olga Smirnova, and Misha Ivanov of the Berlin Max Born Institute, however, have now devised a method that will, in the truest sense, shed light on the process. Their theory involves firing extremely short, tailored laser pulses at a material - pulses that can only recently be produced in the appropriate quality given the latest developments in lasers. One then observes the material's reaction to these pulses to see how the electrons in the material are excited into motion and, like a bell, emit resonant vibrations at specific frequencies, as harmonics of the incident light.

"By analysing this high harmonic spectrum, we can observe the change in the structural order in these strongly correlated materials 'live' for the first time," says first author of the paper Rui Silva of the Max Born Institute. Laser sources capable of targetedly triggering these transitions have only been available since very recently. The laser pulses namely have to be amply strong and extremely short - on the order of femtoseconds in duration (millionths of a billionth of a second).

In some cases, it takes only a single oscillation of light to disrupt the electronic order of a material and turn an insulator into a metal-like conductor. The scientists at the Berlin Max Born Institute are among the world's leading experts in the field of ultrashort laser pulses.

"If we want to use light to control the properties of electrons in a material, then we need to know exactly how the electrons will react to light pulses," Ivanov explains. With the latest-generation laser sources, which allow full control over the electromagnetic field even down to a single oscillation, the newly published method will allow deep insights into the materials of the future.

NautePhotonics
Fig. (click to enlarge)

High harmonic spectroscopy of light-induced phase transition. The vertical red line shows when the laser electric field (yellow oscillating curve) crosses the threshold field, destroying the insulating phase of the material. The top panel shows the average number of doublon-hole pairs per site (blue) and the decay of the insulating field-free ground state (red). (Source: MBI)


Original publication:
"High harmonic spectroscopy of ultrafast many-body dynamics in strongly correlated systems"

R. E. F. Silva, Igor V. Blinov, Alexey N. Rubtsov, O. Smirnova & M. Ivanov
Nature Photonics, (2018) (online), DOI: 10.1038/s41566-018-0129-0

Contact:

Prof. Dr. Misha Ivanov, Tel. 030 / 6392 1210
Prof. Dr. Olga Smirnova, Tel.: 030 6392 1340
Dr. R.E.F. Silva, Tel.: 030 6392 1239

 
     
 


Wiggling atoms switch the electric polarization of crystals

12 April 2018

Ferroelectric crystals display a macroscopic electric polarization, a superposition of many dipoles at the atomic scale which originate from spatially separated electrons and atomic nuclei. The macroscopic polarization is expected to change when the atoms are set in motion but the connection between polarization and atomic motions has remained unknown. A time-resolved x-ray experiment now elucidates that tiny atomic vibrations shift negative charges over a 1000 times larger distance between atoms and switch the macroscopic polarization on a time scale of a millionth of a millionth of a second.

Ferroelectric materials have received strong interest for applications in electronic sensors, memories, and switching devices. In this context, fast and controlled changes of their electric properties are essential for implementing specific functions efficiently. This calls for understanding the connection between atomic structure and macroscopic electric properties, including the physical mechanisms governing the fastest possible dynamics of macrosopic electric polarizations.

Researchers from the Max-Born-Institute in Berlin have now demonstrated how atomic vibrations modulate the macroscopic electric polarization of the prototype ferroelectric ammonium sulphate [Fig. 1] on a time scale of a few picoseconds (1 picosecond (ps) = 1 millionth of a millionth of a second). In the current issue of the journal Structural Dynamics [5, 024501 (2018)], they report an ultrafast x-ray experiment which allows for mapping the motion of charges over distances on the order of the diameter of an atom (10-10m = 100 picometers) in a quantitative way. In the measurements, an ultrashort excitation pulse sets the atoms of the material, a powder of small crystallites, into vibration. A time-delayed hard x-ray pulse is diffracted from the excited sample and measures the momentary atomic arrangement in form of an x-ray powder diffraction pattern. The sequence of such snapshots represents a movie of the so-called electron-density map from which the spatial distribution of electrons and atomic vibrations are derived for each instant in time ([Fig. 2], [Movie]).

The electron density maps show that electrons move over distances of 10-10m between atoms which are more than a thousand times larger than their displacements during the vibrations [Fig. 3]. This behavior is due to the complex interplay of local electric fields with the polarizable electron clouds around the atoms and determines the momentary electric dipole at the atomic scale. Applying a novel theoretical concept, the time-dependent charge distribution in the atomic world is linked to the macroscopic electric polarization [Fig. 3]. The latter is strongly modulated by the tiny atomic vibrations and fully reverses its sign in time with the atomic motions. The modulation frequency of 300 GHz is set by the frequency of the atomic vibrations and corresponds to a full reversal of the microscopic polarization within 1.5 ps, much faster than any existing ferroelectric switching device. At the surface of a crystallite, the maximum electric polarization generates an electric field of approximately 700 million volts per meter.

The results establish time-resolved ultrafast x-ray diffraction as a method for linking atomic-scale charge dynamics to macroscopic electric properties. This novel strategy allows for testing quantum-mechanical calculations of electric properties and for characterizing a large class of polar and/or ionic materials in view of their potential for high-speed electronics.

PM_Fig1
Fig. 1 (click to enlarge)

Fig. 1: Crystal lattice of ferroelectric ammonium sulfate [(NH4)2SO4] with tilted ammonium (NH4+) tetrahedra (nitrogen: blue, hydrogen: white) and sulfate (SO42-) tetrahedra (sulfur: yellow, oxygen: red). The green arrow shows the direction of macroscopic polarization P. Blue arrows: local dipoles between sulphur and oxygen atoms. The electron density maps shown in the bottom left panel, in Fig. 2, and the movie are taken in the plane shown in grey. Bottom left: Stationary electron density of sulfur and oxygen atoms, displaying high values on the sulfur (red) and smaller values on the oxygens (yellow). Bottom right: Change of local dipoles at a delay time of 2.8 picoseconds (ps) after excitation of the ammonium sulfate crystallites. An anisotropic shift of charge reduces the dipole pointing to the right and increases the other 3 dipoles.

PM_Fig2
Fig. 2 (click to enlarge)
Fig 2: (a) Stationary electron density in the grey plane shown in Fig. 1. (b) Change of electron density at a delay time of 2.8 picoseconds (ps) after excitation of the ammonium sulfate crystallites. The circles mark the atomic positions, the black arrows indicate the transfer of electronic charge between one of the oxygen atom and the SO3 group of a single sulfate ion. The vibrational displacements of the atoms are smaller than the line thickness of the circles and, thus, invisible on this length scale. (c) The reverse charge transfer occurs at a delay time of 3.9 ps.
Movie_GIF
Movie (click to enlarge)
Movie: The movie shows the entire temporal evolution of the electron density map.
PM_Fig3
Fig. 3 (click to enlarge)
Fig 3: Upper panel: Change of the S-O bond length as a function of the delay time. The maximum change of 0.1 pm is 1000 times smaller than the bond length itself, i.e., the atomic motions cannot be observed in Fig. 2. Middle panel: Charge transfer from one oxygen atom to the SO3 group of the sulfate ion (left black arrows in Fig. 2) as a function of delay time. Lower panel: Change of the macroscopic polarization P along the c axis which is the sum of all microscopic dipole changes of the local S-O dipoles within the sulfhate ions (red and blue arrows in Fig. 1 bottom right).

Original article:
Christoph Hauf, Antonio-Andres Hernandez Salvador, Marcel Holtz, Michael Woerner, and Thomas Elsaesser, Soft-mode driven polarity reversal in ferroelectrics mapped by ultrafast x-ray diffraction, Struct. Dyn. 5, 024501 (2018).

Further information:
Dr. Michael Wörner, Tel.: 030 6392 1470
Dr. Christoph Hauf, Tel.: 030 6392 1473
Prof. Dr. Thomas Elsaesser, Tel.: 030 6392 1400

 

 

 
     
 


X-ray snapshots of reacting acids and bases - Erik T. J. Nibbering receives an ERC Advanced Grant for groundbreaking basic research

9 April 2018

Dr. Erik T. J. Nibbering of the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin receives an Advanced Grant from the European Research Council (ERC). Goal with this prestigious award is to investigate and elucidate the elementary steps of aqueous proton transfer dynamics between acids and bases. The ERC Advanced Grant is endowed with 2.5 million euro and awarded to well-established top researchers in Europe pursuing scientifically excelling projects.

Dr. Erik T. J. Nibbering, head of the department "Femtosecond Spectroscopy of Molecular Systems" at MBI, has a major track record in time-resolved spectroscopy of ultrafast chemical reactions, in particular proton transfer between acids and bases, electron transfer in donor-acceptor complexes, and trans/cis isomerization. In recent years his activities have focused on the dynamics of the hydrogen bond structure of photoacid-base complexes and of hydrated protons.

How acids and bases react in water is a question raised since the pioneering days of modern chemistry. Recent decades have witnessed an increased effort in elucidating the microscopic mechanisms of proton exchange between acids and bases and the important mediating role of water in this. With ultrafast spectroscopy it has been shown that the elementary steps in aqueous proton transfer occur on femtosecond to picosecond time scales (1 femtosecond = 10-15 s = 1 millionth of a billionth of a second). Aqueous acid-base neutralization predominantly proceeds in a sequential way via water bridging acid and base molecules. These ultrafast experiments probing molecular transitions in the ultraviolet, visible and mid-infrared spectral ranges, though, only provide limited insight into the electronic structure of acids, bases and the water molecules accommodating the transfer of protons in the condensed phase. Soft-x-ray absorption spectroscopy (XAS), probing transitions from inner-shell levels to unoccupied molecular orbitals, is a tool to monitor electronic structure with chemical element specificity.

The aim is now to develop steady-state and time-resolved soft-x-ray spectroscopy of acids and bases. Here novel liquid flatjet technology is utilized with soft-x-ray sources at synchrotrons as well as table-top laser-based high-order harmonic systems. Resolving the electronic structural dynamics of elementary steps of aqueous proton transport will furthermore elucidate the role of mediating water in bulk solution, and in specific conditions such as hydrogen fuel cells or trans-membrane proteins.

Further information on Dr. Erik T. J. Nibbering can be found at http://staff.mbi-berlin.de/nibberin/ and on ERC Grants at http://erc.europa.eu/.

Contact:
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI)
Dr. Erik T. J. Nibbering
Phone +49 / 30 / 6392-1477

 

 

 
     
 


A spinning top of light

27 February 2018

Short, rotating pulses of light reveal a great deal about the inner structure of materials. An international team of physicists led by Prof. Misha Ivanov of the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) has now developed a new method for precisely characterising such extremely short light pulses. The research results have been published in Nature Communications.

Not all light is equal: depending on how it is prepared, it can exist in very different forms. Not only can we choose different wavelengths or colours but, as an electromagnetic wave, light can also exhibit different forms of oscillation. It can occur in different polarisations, for example - either linearly polarised or circularly polarised, where the oscillations of the electromagnetic fields follow a line or go round in circles, respectively. Above all, extremely short pulses of polarised light waves are excellent for studying many different types of materials. We have methods for producing such pulses, but these methods are already pushing the limits of technical feasibility and the light pulses are not always produced with the desired properties.

A new method now allows us to characterise these short light pulses with unprecedented precision. The trouble starts with the fact that the processes of interest taking place inside matter, which we would like to study with our light pulses, are extremely short-lived. Accordingly, the light pulses have to be similarly short, in the range of around 100 attoseconds (billionths of a billionth of a second). In this unimaginably short timespan, a light wave can only undergo a few rotations. Even using the latest laser methods to produce such ultrashort pulses, it can easily happen that the light wave will not come out rotating the right way.

The concept for the new method can be described as follows: one fires an extremely short, high-energy and circularly polarised light pulse at an atom or a solid body where, upon being absorbed, the light pulse knocks an electron out of the body. This electron then carries information about the light wave itself and can furthermore reveal clues as to the properties of the sample being examined. Because the light pulses are circularly polarised, the ejected electrons also fly off with a rotating motion.

"You can compare the electrons being ejected with a one-armed sprinkler, which either continues turning in the direction you want it to, or which keeps stuttering and even changing its direction," says Misha Ivanov, Head of the Theory Department of the Max Born Institute. If the sprinkler is allowed to run for a while, then it will wet the grass in a full circle - irrespective of whether it rotates consistently or not. So, merely looking at the grass will not reveal whether the sprinkler has been turning exactly the way it was desired or not. "But if a gusty wind comes along, then we can distinguish whether the sprinkler has been turning regularly or irregularly," Ivanov says. If the wind blows alternately from the left or right each time the arm of the sprinkler faces left or right, then the patch of wet grass will not be circular, but rather elliptical in shape. A sprinkler rotating completely irregularly would magically conjure up an ellipse on the grass stretched in the wind direction, while a regularly rotating sprinkler will display a tilted ellipse.

This "wind" is added into the experiment in the form of an infrared laser pulse whose oscillations are perfectly synchronised with the ultrashort pulses. The infrared radiation accelerates the electron either to the left or right - just like the wind blows the water droplets.

"By measuring the electrons, we can then determine whether the light pulse possessed the desired consistent rotation or not," says the first author of the publication in "Nature Communications", researcher Álvaro Jiménez-Galán of the Max Born Institute. "Our method allows one to characterise the properties of the ultrashort light pulses with unprecedented precision," Jiménez-Galán adds. And the more precisely these light pulses are characterised, the more detailed information can be derived about the electron's place of origin within an exotic material.

This is of special significance when it comes to studying a whole series of novel materials. These could include superconductors, which can conduct electricity without electrical resistance, or topological materials that exhibit exotic behaviour, the research of which earned a Nobel Prize in Physics in 2016. Materials like these could be used to make a quantum computer, for example, or could allow superfast, energy-efficient processors and memory chips to be built into normal computers and smartphones.

The new sprinkler method still only exists in theory for the moment, but ought to be implementable in the near future. "Our requirements are fully within the latest state of the art, so there is nothing to preclude this from being realised soon," Ivanov asserts.

SmirnovaPanel

Fig. 1 (click to enlarge)

Fig.:

Left alone, the circular sprinkler distributes the water evenly, and the grass grows in a circular pattern regardless of whether the sprinkler rotates clock-wise, counter-clockwise, or randomly. If wind blows, the grass is watered unevenly, as seen in its growth. If the wind blows in a regular pattern, changing its strength with clock-work precision, the asymmetry in the grass growth allows us to reconstruct the properties of the sprinkler, distinguishing the precision-made, regularly rotating sprinkler from a randomly oscillating cheap version.

In our micro-world setup, the sprinkler is the short pulse (in blue), lasting only about 10-16 sec, with its electric field rotating even faster in an unknown pattern. The wind is a linearly polarized and precisely controlled infrared laser field (in red). The grass is the measured photoelectron angular distribution (in green). The asymmetry in the latter allows us to reconstruct, for the first time, the polarization properties of the ultra-short pulse that lasts about 10-16 sec. (Figure credit: Felipe Morales und Álvaro Jiménez-Galán)

Original Publication: Nature Communications
Álvaro Jiménez-Galán, Gopal Dixit, Serguei Patchkovskii, Olga Smirnova, Felipe Morales & Misha Ivanov: Attosecond recorder of the polarization state of light
Nature Communications, volume 9, Article number: 850 (2018), doi:10.1038/s41467-018-03167-2

Contact

Prof. Dr. Misha Ivanov, Tel.: 030 6392 1340

Prof. Dr. Álvaro Jiménez-Galán, Tel.: 030 6392 1340

Prof. Dr. Olga Smirnova, Tel.: 030 6392 1340

 

 

 
     
 


C'mon electrons, let's do the twist! Twisting electrons can tell right-handed and left-handed molecules apart.

19 February 2018

Identifying right-handed and left-handed molecules is a crucial step for many applications in chemistry and pharmaceutics. An international research team (CELIA-CNRS/INRS/Berlin Max Born Institute/SOLEIL) has now presented a new original and very sensitive method. The researchers use laser pulses of extremely short duration to excite electrons in molecules into twisting motion, the direction of which reveals the molecules' handedness. The research results appear in Nature Physics.

Are you right handed or left handed? No, we aren't asking you, dear reader; we are asking your molecules. It goes without saying that, depending on which hand you use, your fingers will wrap either one way or the other around an object when you grip it. It so happens that this handedness, or "chirality", is also very important in the world of molecules. In fact, we can argue that a molecule's handedness is far more important than yours: some substances will be either toxic or beneficial depending on which "mirror-twin" is present. Certain medicines must therefore contain exclusively the right-handed or the left-handed twin.

The problem lies in identifying and separating right-handed from left-handed molecules, which behave exactly the same unless they interact with another chiral object. An international research team has now presented a new method that is extremely sensitive at determining the chirality of molecules.

We have known that molecules can be chiral since the 19th century. Perhaps the most famous example is DNA, whose structure resembles a right-handed corkscrew. Conventionally, chirality is determined using so-called circularly polarised light, whose electromagnetic fields rotate either clockwise or anticlockwise, forming a right or left "corkscrew", with the axis along the direction of the light ray. This chiral light is absorbed differently by molecules of opposite handedness. This effect, however, is small because the wavelength of light is much longer than the size of a molecule: the light's corkscrew is too big to sense the molecule's chiral structure efficiently.

The new method, however, greatly amplifies the chiral signal. "The trick is to fire a very short, circularly polarized laser pulse at the molecules," says Olga Smirnova from the Max Born Institute. This pulse is only some tenths of a trillionth of a second long and transfers energy to the electrons in the molecule, exciting them into helical motion. The electrons' motion naturally follows a right or left helix in time depending on the handedness of the molecular structure they reside in.

Their motion can now be probed by a second laser pulse. This pulse also has to be short to catch the direction of electron motion and have enough photon energy to knock the excited electrons out of the molecule. Depending on whether they were moving clockwise or anticlockwise, the electrons will fly out of the molecule along or opposite to the direction of the laser ray.

This lets the experimentalists of CELIA to determine the chirality of the molecules very efficiently, with a signal 1000 times stronger than with the most commonly used method. What's more, it could allow one to initiate chiral chemical reactions and follow them in time. It comes down to applying very short laser pulses with just the right carrier frequency. The technology is a culmination of basic research in physics and has only been available since recently. It could prove extremely useful in other fields where chirality plays an important role, such as chemical and pharmaceutical research.

Having succeeded in identifying the chirality of molecules with their new method, the researchers are now thinking already of developing a method for laser separation of right- and left-handed molecules. Text: Dirk Eidemueller/Forschungsverbund Berlin e.V. - Translation: Peter Gregg

FingBru_fig_1

Fig. (click to enlarge)

Fig: Following excitation by an ultra-short circularly polarised laser pulse, electrons follow a right or left helix depending on the handedness of the molecular structure they reside in. Source: Samuel Beaulieu

Original Publication: Nature Physics
S. Beaulieu, A. Comby, D. Descamps, B. Fabre, G. A. Garcia, R. Géneaux, A. G. Harvey, F. Légaré, Z. Mašin, L. Nahon, A. F. Ordonez, S. Petit, B. Pons, Y. Mairesse, O. Smirnova and V. Blanchet: Photoexcitation Circular Dichroism in Chiral Molecules
Nature Physics (2018) online, doi:10.1038/s41567-017-0038-z.

Contact

Prof. Dr. Olga Smirnova, Tel.: 030 6392 1340

 

 

 
     
 


Flexibility and arrangement - the interaction of ribonucleic acid and water

16 January 2018

Ribonucleic acid (RNA) plays a key role in biochemical processes which occur at the cellular level in a water environment. Mechanisms and dynamics of the interaction between RNA and water were now revealed by vibrational spectroscopy on ultrashort time scales and analyzed by in-depth theory

Ribonucleic acid (RNA) represents an elementary constituent of biological cells. While deoxyribonucleic acid (DNA) serves as the carrier of genetic information, RNA displays a much more complex biochemical functionality. This includes the transmission of information in the form of mRNA, RNA-mediated catalytic function in ribosomes, and the encoding of genetic information in viruses. RNA consists of a sequence of organic nucleobase molecules which are held together by a so-called backbone consisting of phosphate and sugar groups. Such a sequence can exist as a single strand or in a paired double-helix geometry. Both forms are embedded in a water shell and their phosphate and sugar groups are distinct docking points for water molecules. The structure of the water shell fluctuates on a time scale of a few tenth of a picosecond (1 ps = 10-12 s = 1 millionth of a millionth of a second). The interactions of RNA and water and their role for the formation of three-dimensional RNA structures are only understood insufficiently and difficult to access by experiment.

Scientists from the Max Born Institute have now observed the interaction of RNA with its water shell in real time. In their new experimental method, vibrations of the RNA backbone serve as sensitive noninvasive probes of the influence of neighboring water molecules on the structure and dynamics of RNA. The so-called two-dimensional infrared spectroscopy allows for mapping the time evolution of vibrational excitations and for determining molecular interactions within RNA and between RNA and water. The results show that water molecules at the RNA surface perform tipping motions, so-called librations, within a fraction of a picosecond whereas their local spatial arrangement is preserved for a time range longer than 10 ps. This behavior deviates strongly from that of neat water and is governed by the steric boundary conditions set by the RNA surface. Individual water molecules connect neighboring phosphate groups and form a partly ordered structure which is mediated by their coupling to the sugar units.

The librating water molecules generate an electrical force by which the water fluctuations are transferred to the vibrations of RNA. The different backbone vibrations display a diverse dynamical behavior which is determined by their local water environment and reflects its heterogeneity. RNA vibrations also couple mutually and exchange energy among themselves and with the water shell. The resulting ultrafast redistribution of excess energy is essential for avoiding a local overheating of the sensitive macromolecular structure. This complex scenario was analyzed by detailed theoretical calculations and simulations which, among other results, allowed for the first complete and quantitative identification of the different vibrations of the RNA backbone. Comparative experiments with DNA reveal similarities and characteristic differences between these two elementary biomolecules, showing a more structured water arrangement around RNA. The study highlights the strong potential of non-invasive time-resolved vibrational spectroscopy for unraveling the interplay of structure and dynamics in complex biomolecular systems on molecular length and time scales.

FingBru_fig_1

Fig. 1 (click to enlarge)

Fig. 1: Left: Structure of a RNA double helix. The blue spheres represent sodium counterions. Right: Enlarged segment of the sugar-phosphate backbone of RNA, including bridging water molecules. Vibrations of the RNA backbone serve as sensitive real time probes for mapping the influence of the neighboring water molecules on RNA's structure and dynamics.


Fig. 2 (click to enlarge)
Fig. 2: Two-dimensional vibrational spectra of RNA (upper panel) and DNA (lower panel) in the frequency range of the sugar-phosphate vibrations of the backbone. The RNA spectrum displays additional bands (contours) along the frequency diagonal ν13 and a more complex distribution of off-diagonal peaks. In addition to the frequency positions the line shapes of the individual bands (contours) give insight in details of the interactions with neighboring water molecules.

Original publication:
E. M. Bruening, J. Schauss, T. Siebert, B. P. Fingerhut, T. Elsaesser: Vibrational Dynamics and Couplings of the Hydrated RNA Backbone: A Two-Dimensional Infrared Study.
J. Phys. Chem. Lett. 9, 583-587 (2018). DOI: 10.1021/acs.jpclett.7b03314.

Contact:

Dr. Benjamin Fingerhut, Tel.: 030 6392 1404

Prof. Dr. Thomas Elsaesser, Tel.: 030 6392 1400

 

 

 
     
 


Instant x-ray footprints


15 January 2018

MBI scientists together with colleagues from Italy have established a way to detect the exact x-ray fluence footprint generated on a sample by a free electron laser pulse.

Free electron lasers (FELs) deliver intense and coherent x-ray pulses - a prerequisite to investigate and exploit non-linear processes in the interaction of x-rays with matter. Analogous to the development of nonlinear optics after the invention of lasers in the optical regime, the application of these processes is expected to have a widespread impact on numerous research fields. A pivotal parameter in this context is the fluence of the radiation deposited on the sample during a single ultrashort pulse - in essence, the number of photons hitting the sample per unit area for a given photon energy. Unfortunately, this fluence can vary at FELs from shot to shot both in its total amount as well as in the way it is distributed in a focal spot. Simply put, there is a footprint of x-rays on the sample which can vary in both shape and intensity. This makes quantitative experiments on nonlinear processes at x-ray wavelengths very challenging, as they are inherently sensitive to the precise fluence distribution.

Scientists from MBI and the Italian research institutes ELETTRA and IOM have now demonstrated a method, which allows to take a snapshot picture of the fluence distribution impinging on the sample while at the same time recording the scattering signal of interest generated by that very same FEL shot. The approach relies upon the fabrication of very shallow grooves of only a few nanometer depth into the membrane holding the sample. Via a tailored two-dimensional distortion, this groove pattern forms a diffractive optical element that is designed to image the footprint of the incident x-ray beam on a two-dimensional detector. In the figure below, the beam footprint on the sample is visible (in two conjugate copies) as a spot with a checkerboard of many side maxima and minima, while the magnetic scattering from this sample with ferromagnetic domains is visible as a ring on the very same detector. Using this approach, scientists can now relate a scattering signal from a specimen to the exact incident fluence footprint on this sample, as both originate from the identical x-ray pulse.

Furthermore, the use of the grating structure alone - without a sample - turned out to be extremely helpful when aligning the x-ray optics of the FEL or a sample relative to the focal position. Together with the detector, the distorted grating provides instant feedback on the beam shape when placed into the x-ray beam. The new method is already now routinely used at the FERMI free electron laser for alignment purposes.

scattering

Fig. 1 (click to enlarge)

Fig. 1: 2D Detector image downstream of the sample showing both the ring-shaped magnetic scattering as well as the fluence map ("footprint") of x-rays on the sample generating this magnetic scattering.

Original publikation:
M. Schneider, C. M. Günther, B. Pfau, F. Capotondi, M. Manfredda, M. Zangrando, N. Mahne, L. Raimondi, E. Pedersoli, D. Naumenko, and S. Eisebitt, In situ single-shot diffractive fluence mapping for X-ray free-electron laser pulses, Nature Communications 9, 214 (2018).

Contact

Prof. Dr. Stefan Eisebitt, Tel.: 030 6392 1300

 

 
     
 


Marc Vrakking named Editor-in-Chief of the Journal of Physics B

1 January 2018

Prof. Marc Vrakking, director of Division A of the Max Born Institute, has been named Editor-in-Chief of the Journal of Physics B from January 1st 2018. In this capacity he succeeds Prof. Paul Corkum of the University of Ottawa, who served as Editor-in-Chief since 2011.

The Journal of Physics B is one of the publications of the Institute of Physics, and is a prominent journal serving the Atomic, Molecular and Optical (AMO) Physics community. In particular in the emerging fields of strong field physics, attosecond science and free electron laser science the journal has a prominent role, as is manifest by numerous important papers (including Topical Reviews, Tutorials, Special Issues and Roadmaps) that the journal continuously publishes. As such, the journal is strongly aligned with the research program in Division A of the Max Born Institute.

Contact:

Prof. Marc Vrakking Tel. (030) 6392 1200

 
     



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