Forum for Science, Industry and Business

A Quick Look at Electron-Boson Coupling

Imagine being able to tune the properties of a solid material just by flashing pulses of light on it, for example turning an  insulator into a superconductor. That is just one potential payoff down-the-road from the physical phenomenon of electrons and atoms interacting with ultrashort pulses of light.

These trARPES spectra of doped Bi2212 show photoemission intensity before pumping (t= −1 ps) and after pumping (t=1 and t=10 ps). The arrows mark the position of a kink that signifies the coupling of the electrons to bosons.

The technology of ultrafast spectroscopy is a key to understanding this phenomenon and now a new wrinkle to that technology has been introduced by Berkeley Lab researchers.

In a study led by Alessandra Lanzara of Berkeley Lab’s Materials Sciences Division, time- and angle-resolved photoemission spectroscopy (trARPES) was used to directly measure the ultrafast response of electron self-energy – a fundamental quantity used to describe “many-body” interactions in a material – to photo-excitation with near-infrared light in a high-temperature superconductor.

The results demonstrated a link between the phenomena of electron-boson coupling and superconductivity. A boson can be a force-carrying particle, such as a photon, or composite particle of matter, such an atomic nucleus with an even number of protons and neutrons.

“Below the critical temperature of the superconductor, ultrafast excitations triggered a synchronous decrease of electron self-energy and the superconducting energy gap that continued until the gap was quenched,” says Lanzara. “Above the critical temperature of the superconductor, electron–boson coupling was unresponsive to ultrafast excitations. These findings open a new pathway for studying transient self-energy and correlation effects in solids, such as superconductivity.”

The study of electrons and atoms interacting with intense, ultra-short optical pulses is an emerging field of physics because of the roles these interactions play in modulating the electronic structures and properties of materials such as high-temperature superconductors. ARPES has been the long-standing technique of choice for studying the electronic structure of a material.

In this technique, beams of ultraviolet or X-ray light striking the surface or interface of a sample material cause the photoemission of electrons at angles and kinetic energies that can be measured to reveal detailed information about the material’s electronic band structures. While extremely powerful, ARPES lacks the temporal component required for studying band structural dynamics.

Lanzara and a collaboration that included Wentao Zhang, lead author of a paper on this work in Nature Communications, added the necessary temporal component in their trARPES study. They applied this technique to a material known as Bi2212, a compound of bismuth, strontium, calcium, and copper oxide that is considered one of the most promising of high-temperature superconductors.

They energized the Bi2212 samples with femtosecond pulses of near-infrared laser light then probed the results with femtosecond pulses of ultra-violet laser light. The delay time between pump and probe pulses was precisely controlled so that the electron-boson coupling and the superconducting gap could be tracked at the same time.

“In cuprate materials such as Bi2212, there is a known kink in the photoemission pattern that signifies the coupling of the electrons to bosons,” says Zhang. “However, whether this kink is related in any way to superconductivity has been highly debated. Our results show that it is.”

Zhang’s Nature Communications paper, for which Lanzara is the corresponding author, is titled “Ultrafast quenching of electron–boson interaction and superconducting gap in a cuprate.” Other co-authors are Choongyu Hwang, Christopher Smallwood, Tristan Miller, Gregory Affeldt, Koshi Kurashima, Chris Jozwiak, Hiroshi Eisak, Tadashi Adachi, Yoji Koike and Dung-Hai Lee.

This research was supported by the U.S. Department of Energy’s Office of Science.

Additional Information

For more about the research of Alessandra Lanzara go here

Lynn Yarris | Eurek Alert!
Further information:
http://newscenter.lbl.gov/2014/10/06/a-quick-look-at-electron-boson-coupling/

Im Focus: Fraunhofer IDMT demonstrates its method for acoustic quality inspection at »Sensor+Test 2019« in Nürnberg

From June 25th to 27th 2019, the Fraunhofer Institute for Digital Media Technology IDMT in Ilmenau (Germany) will be presenting a new solution for acoustic quality inspection allowing contact-free, non-destructive testing of manufactured parts and components. The method which has reached Technology Readiness Level 6 already, is currently being successfully tested in practical use together with a number of industrial partners.

Reducing machine downtime, manufacturing defects, and excessive scrap

Im Focus: Successfully Tested in Praxis: Bidirectional Sensor Technology Optimizes Laser Material Deposition

The quality of additively manufactured components depends not only on the manufacturing process, but also on the inline process control. The process control ensures a reliable coating process because it detects deviations from the target geometry immediately. At LASER World of PHOTONICS 2019, the Fraunhofer Institute for Laser Technology ILT will be demonstrating how well bi-directional sensor technology can already be used for Laser Material Deposition (LMD) in combination with commercial optics at booth A2.431.

Fraunhofer ILT has been developing optical sensor technology specifically for production measurement technology for around 10 years. In particular, its »bd-1«...

Im Focus: The hidden structure of the periodic system

The well-known representation of chemical elements is just one example of how objects can be arranged and classified

The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...

Im Focus: MPSD team discovers light-induced ferroelectricity in strontium titanate

Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.

Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...

Im Focus: Determining the Earth’s gravity field more accurately than ever before

Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.

The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...