New Advancements in Quantum Critical Material Studies

A team of investigators led by Rice University scientists has recently provided the first-ever evidence that large-scale electronic consequences of “quantum critical” effects exist. The finding came after the group studied a class of materials known as magnetic heavy-fermion metals, which also includes high-temperature superconductors. The physicists, who are based in the United States, Germany and Austria, also report the discovery of a simple “scaling” behavior in the electronic excitations measured in the peculiar metals.

“High-temperature superconductivity has been referred to as the biggest unsolved puzzle in modern physics, and these results provide further support to the idea that correlated electron effects – including high-temperature superconductivity – arise out of quantum critical points,” explains the lead theorist of the group, Rice physicist Qimiao Si. “Our experiments clearly show that variables from classical physics cannot explain all of the observed macroscopic properties of materials at quantum critical points,” explains the director of the Germany-based Max Planck Institute for Chemical Physics of Solids, Frank Steglich. He was the lead experimentalist of the investigation.

Researchers from the Max Planck Institute for the Physics of Complex Systems and the Vienna University of Technology, in Austria, were also involved in the research. All theoretical and experimental results the international group arrived at have been published in the latest issue of the esteemed journal Proceedings of the National Academy of Sciences (PNAS). The science group reveals that the studies were conducted on a material called YbRh2Si2 (YRS). This is a combination of ytterbium, rhodium and silicon that represents one of the most studied quantum critical materials.

“The experiments provide, for the first time, the evidence for a salient property of local quantum criticality, namely the driving force for dynamical scaling is the Fermi-volume [combined wavelengths of all the electrons in a crystalline solid] collapse, even though the quantum transition is magnetic,” explains the head of the VUT Institute of Solid State Physics, Silke Paschen. The professor is also a coauthor of the PNAS paper. Other co-authors include Sven Friedmann, Niels Oeschler, Steffen Wirth, Cornelius Krellner and Christoph Geibel, all of the Max Planck Institute for Chemical Physics of Solids, and Stefan Kirchner, a former postdoctoral fellow at the Rice University.