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 Turning entanglement upside down
22.05.2018 | Universität Innsbruck

nachricht Astronomers release most complete ultraviolet-light survey of nearby galaxies
18.05.2018 | NASA/Goddard Space Flight Center

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: LZH showcases laser material processing of tomorrow at the LASYS 2018

At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.

At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...

Im Focus: Self-illuminating pixels for a new display generation

There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?

At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

Im Focus: Dozens of binaries from Milky Way's globular clusters could be detectable by LISA

Next-generation gravitational wave detector in space will complement LIGO on Earth

The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...

Im Focus: Entangled atoms shine in unison

A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.

The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

 
Latest News

Designer cells: artificial enzyme can activate a gene switch

22.05.2018 | Life Sciences

PR of MCC: Carbon removal from atmosphere unavoidable for 1.5 degree target

22.05.2018 | Earth Sciences

Achema 2018: New camera system monitors distillation and helps save energy

22.05.2018 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>