Physicists explore mysteries of strange metals

Physicists are learning more about the strange behavior of “strange metals,” which operate outside the normal rules of electricity.

Theoretical physicist Yashar Komijani, an assistant professor at the University of Cincinnati, contributed to an international experiment using a strange metal made from an alloy of ytterbium, a rare earth metal. Physicists at a laboratory in Hyogo, Japan, fired radioactive gamma rays at the strange metal to observe its unusual electrical behavior.

Led by Hisao Kobayashi with Hyogo University and RIKEN, the study was published in the journal Science. The experiment revealed unusual variations in the strange metal’s electrical charge.

“The idea is that in a metal, you have a sea of ​​electrons moving deep into a lattice of ions,” Komijani said. “But a wonderful thing happens with quantum mechanics. You can forget about the lattice complications of ions. Instead, they behave as if they were in a vacuum.”

Komijani has been exploring the mysteries of strange metals in relation to quantum mechanics for years.

“You can put something in a black box and I can tell you a lot about what’s inside it without even looking at it just by measuring things like resistivity, heat capacity and conductivity,” he said.

“But when it comes to strange metals, I have no idea why they behave the way they do. The mystery is what’s going on inside that strange system. That’s the question.”

Strange metals are of interest to a wide range of physicists who study everything from particle physics to quantum mechanics. One reason is their strangely high conductivity, at least at extremely low temperatures, which gives them potential as superconductors for quantum computing.

“The thing that’s really exciting about these new results is that they provide new insight into the inner mechanism of the strange metal,” said study co-author Piers Coleman, distinguished professor at Rutgers University.

“These metals provide the canvas for new forms of electronic matter – particularly exotic and high-temperature superconductivity,” he said.

Coleman said it’s too early to speculate about what new technologies the strange metals might inspire.

“It is said that after Michael Faraday discovered electromagnetism, British Chancellor William Gladstone asked what he would be good at,” Coleman said. “Faraday replied that while he did not know, he was sure that one day the government would tax it.”

Faraday’s discoveries opened up a world of innovation.

“We kind of feel the same way about the odd metal,” Coleman said. “Metals play such a central role today – copper, the archetypal conventional metal, is in all appliances, all power lines, all around us.”

Coleman said that strange metals could one day be just as ubiquitous in our technology.

Japan’s experiment was groundbreaking in part because of the way the researchers created the gamma particles using a particle accelerator called a synchrotron.

“In Japan they use a synchrotron like at CERN [the European Organization for Nuclear Research] that accelerates a proton and smashes it into a wall and emits a gamma ray,” Komijani said. “So they have an on-demand source of gamma rays without using radioactive material.”

The researchers used spectroscopy to study the effects of gamma rays on the strange metal.

The researchers also looked at the speed of the metal’s electrical charge fluctuations, which take just a nanosecond—a billionth of a second. That might seem incredibly fast, Komijani said.

“However, in the quantum world, a nanosecond is an eternity,” he said. “For a long time we wondered why these fluctuations are actually so slow. We theorized with collaborators that there might be lattice vibrations, and indeed they did.”