Quantum fractals at the border of magnetism

U.S., German and Austrian physicists studying the perplexing class of materials that includes high-temperature superconductors are reporting this week the unexpected discovery of a simple "scaling" behavior in the electronic excitations measured in a related material. The experiments, which were conducted on magnetic heavy-fermion metals, offer direct evidence of the large-scale electronic consequences of "quantum critical" effects.

The experimental and theoretical results are reported this week in the Proceedings of the National Academy of Science by physicists at Rice University in Houston; the Max Planck Institute for Chemical Physics of Solids and the Max Planck Institute for the Physics of Complex Systems, both in Dresden, Germany; and the Vienna University of Technology in Austria.

"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," said Rice physicist Qimiao Si, the group's lead theorist.

"Our experiments clearly show that variables from classical physics cannot explain all of the observed macroscopic properties of materials at quantum critical points," said lead experimentalist Frank Steglich, director of the Max Planck Institute for Chemical Physics of Solids.

The experiments by Steglich's group were conducted on a heavy-fermion metal containing ytterbium, rhodium and silicon that is known as YbRh2Si2 (YRS). YRS is one of the best-characterized and most-studied quantum critical materials.

Quantum criticality refers to a phase transition, or tipping point, that marks an abrupt change in the physical properties of a material. The most common example of an everyday phase change would be the melting of ice, which marks the change of water from a solid to a liquid phase. The term "quantum critical matter" refers to any material that undergoes a phase transition due solely to the jittering of subatomic particles as described by Heisenberg’s uncertainty principle. Heavy-fermion metals like YRS are one such material class, and considerable evidence exists that high-temperature superconductors are another.

Scientists are keen to better understand high-temperature superconductivity because the technology could revolutionize electric generators, MRI scanners, high-speed trains and other devices. ...

via Rice University | News & Media.