Classical and high-temperature superconductors differ hugely in the value of the critical temperatures at which they lose all electrical resistance.
This image shows Mathieu Le Tacon (foreground) and Alexeï Bosak (background) mounting a sample on beamline ID28 of the ESRF where the X-ray experiments were performed.
Credit: ESRF/Blascha Faust
This image shows the result of diffuse scattering on the high-temperature superconductor, which is the first of the two stages in the experiment. The coloured areas enable to identify the wavelength of the phonons where the coupling with the electrons is taking place.
Credit: MPI Stuttgart/M. Le Tacon
Scientists have now used powerful X-rays to establish another big difference: high-temperature superconductivity cannot be accounted for by the mechanism that leads to conventional superconductivity.
As this mechanism called "electron-phonon coupling" contributes only marginally to the loss of electrical resistance, other scenarios must now be developed to explain high-temperature superconductivity. The results are published on 24 November 2013 in Nature Physics.
The team of scientists was led by Mathieu Le Tacon and Bernhard Keimer from the Max-Planck-Institute for Solid State Research in Stuttgart (Germany) and comprised scientists from Politecnico di Milano (Italy), Karlsruhe Institute of Technology (KIT) and the European Synchrotron (ESRF) in Grenoble, France.
High-temperature superconductivity was discovered nearly thirty years ago and is beginning to find more and more practical applications. These materials have fascinated scientists since their discovery. For even more practical applications, the origin of their amazing properties must be understood, and ways found to calculate the critical temperature. A key element of this understanding is the process that makes electrons combine into so-called "Cooper pairs" when the material is cooled below the critical temperature. In classical superconductors, these Cooper pairs are formed thanks to electron-phonon coupling, an interaction between electrons carrying the electrical current and collective vibrations of atoms in the material.
To understand the role this interaction plays in high-temperature superconductors, Matthieu Le Tacon and his colleagues took up the challenge to study these atomic vibrations as the material was cooled down below its critical temperature.
"Studying electron-phonon coupling in these superconductors is always a delicate task, due to the complex structure of the materials," says Alexeï Bosak, an ESRF scientist and member of the team. He adds: "This is why we developed a two-level approach to literally find a needle in the hay stack".
The big surprise came once the electron-phonon coupling had been probed. "In terms of its amplitude, the coupling is actually by far the biggest ever observed in a superconductor, but it occurs in a very narrow region of phonon wavelengths and at a very low energy of vibration of the atoms", adds Mathieu Le Tacon. "This explains why nobody could see it before the two-level approach of X-ray scattering was developed".
Because the electron-phonon coupling is in such a narrow wavelength region, it cannot "help" two electrons to bind themselves together into a Cooper pair. The next step will be to make systematic observations in many other high-temperature superconductors. "Although we now know that electron-phonon coupling does not contribute to their superconductivity, the unexpected size of the effect—we call it giant electron-phonon-coupling—happens to be a valuable tool to study the interplay between superconductivity and other competing processes. This will hopefully provide further insight into the origin of high-temperature superconductivity, still one of the big mysteries of science", concludes Mathieu Le Tacon.
Claus Habfast | EurekAlert!
Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology
NASA team finds noxious ice cloud on saturn's moon titan
19.10.2017 | NASA/Goddard Space Flight Center
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
19.10.2017 | Materials Sciences
19.10.2017 | Materials Sciences
19.10.2017 | Physics and Astronomy