Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Laser pulses help scientists tease apart complex electron interactions

20.12.2016

Time-resolved “stop-action” measurements and advanced theoretical simulations identify an unusual form of energy loss

Understanding the properties of complex quantum materials is a major goal of condensed matter physics and materials science, since effects like high-temperature superconductivity might lead to a broad range of applications.


A first laser pulse excites a solid; a second pulse knocks out electrons that travel to a detector. The resulting pictures allow scientists to learn about fundamental interactions inside the solid.

© Brian Moritz / SLAC

Now an international team of scientists including Emmy Noether group leader Michael Sentef from the Max Planck Institute for the Structure and Dynamics of Matter at CFEL in Hamburg has demonstrated a new laser-driven “stop-action” technique for studying complex electron interactions under dynamic conditions. The findings, published in the journal Nature Communications today, are expected to improve the understanding of the physical processes leading to emergent phenomena in strongly correlated materials.

Scientists studying high temperature superconductors—materials that carry electric current with no energy loss when cooled below a certain temperature—have been searching for ways to study in detail the electron interactions thought to drive this promising property. One big challenge is disentangling the many different types of interactions—for example, separating the effects of electrons interacting with one another from those caused by their interactions with the atoms of the material.

In the present study, the researchers used one very fast, intense “pump” laser to give electrons a blast of energy, and a second “probe” laser to measure the electrons’ energy level and direction of movement as they relax back to their normal state.

“By varying the time between the ‘pump’ and the ‘probe’ laser pulses we can build up a stroboscopic record of what happens—a movie of what this material looks like from rest through the violent interaction to how it settles back down,” said Jonathan Rameau, physicist at the Brookhaven National Laboratory and one of the lead authors on the paper. “It’s like dropping a bowling ball in a bucket of water to cause a big disruption, and then taking pictures at various times afterward,” he explained.

The technique, known as time-resolved, angle-resolved photoelectron spectroscopy (tr-ARPES), combined with complex theoretical simulations and analysis, allowed the team to tease out the sequence and energy “signatures” of different types of electron interactions. They were able to pick out distinct signals of interactions among excited electrons (which happen quickly, but don’t dissipate much energy), as well as later-stage random interactions between electrons and the atoms that make up the crystal lattice (which generate friction and lead to gradual energy loss in the form of heat).

But they also discovered another, unexpected signal—which they say represents a distinct form of extremely efficient energy loss—at a particular energy level and timescale between the other two.

“We see a very strong and peculiar interaction between the excited electrons and the lattice, where the electrons are losing most of their energy very rapidly in a coherent, non-random way,” Rameau said. At this special energy level, he explained, the electrons appear to be interacting with lattice atoms all vibrating at a particular frequency—like a tuning fork emitting a single note.

When all of the electrons that have the energy required for this unique interaction have given up most of their energy, they start to cool down more slowly by hitting atoms more randomly without striking the resonant frequency, he said. The resonance frequency of this process is particularly noteworthy, the scientists say, because its energy level corresponds with a “kink” in the energy signature of the same material studied previously in its superconducting state using a static form of ARPES.

At that time, scientists suspected the kink might have something to do with the material’s ability to become a superconductor. They couldn’t detect the same signal above the superconducting temperature. But the new time-resolved experiments, which were done on the material well above its superconducting temperature, were able to tease out the subtle signal. These new findings indicate that this special condition exists even when the material is not a superconductor. “We know now that this interaction doesn’t just switch on when the material becomes a superconductor; it’s actually always there,” Rameau said.

Michael Sentef, who complemented the experimental work with numerical simulations, stressed the impact of this work for the field of pump-probe spectroscopy. “This work highlights the fact that we have advanced our theoretical understanding of systems far from thermal equilibrium to the point where we can make quantitative predictions for experiments,” he said. “This insight is very motivating for future work addressing even more complex situations, in which laser pulses are used to induce high-temperature superconducting-like states,” Sentef added. In a recent work [Mitrano et al., Nature 530, 461–464 (2016)], a team around Andrea Cavalleri from the MPSD at CFEL in Hamburg observed light-induced superconducting-like properties in the material K3C60.

Contact person:

Dr. Michael A. Sentef
Max Planck Institute for the Structure and Dynamics of Matter
Center for Free-Electron Laser Science
Luruper Chaussee 149
22761 Hamburg
Germany
+49 (0)40 8998-6552
michael.sentef@mpsd.mpg.de

Original publication:

J. D. Rameau, S. Freutel, A. F. Kemper, M. A. Sentef, J. K. Freericks, I. Avigo, M. Ligges, L. Rettig, Y. Yoshida, H. Eisaki, J. Schneeloch, R. D. Zhong, Z. J. Xu, G. D. Gu, P. D. Johnson, and U. Bovensiepen, "Energy Dissipation from a Correlated System Driven Out of Equilibrium," Nature Communications (2016), DOI: 10.1038/ncomms13761

Weitere Informationen:

http://dx.doi.org/10.1038/ncomms13761 Original publication
http://dx.doi.org/10.1038/nature16522 Mitrano et al., Nature 530, 461–464 (2016)
http://www.mpsd.mpg.de/en/research/theo Research group of Prof. Angel Rubio
http://www.mpsd.mpg.de/en Max Planck Institute for the Structure and Dynamics of Matter

Dr. Michael Grefe | Max-Planck-Institut für Struktur und Dynamik der Materie

Further reports about: Dynamik Electrons Laser Max Planck Institute Max-Planck-Institut laser pulses

More articles from Physics and Astronomy:

nachricht NASA's James Webb Space Telescope completes final cryogenic testing
21.11.2017 | NASA/Goddard Space Flight Center

nachricht Previous evidence of water on mars now identified as grainflows
21.11.2017 | US Geological Survey

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Previous evidence of water on mars now identified as grainflows

21.11.2017 | Physics and Astronomy

NASA's James Webb Space Telescope completes final cryogenic testing

21.11.2017 | Physics and Astronomy

New catalyst controls activation of a carbon-hydrogen bond

21.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>