Elemental superconductor reveals new physics under pressure 

Superconductivity, in which electrons flow with zero resistance, has long defied simple explanation.  

In 1997, a team led by UIC scientist Russell Hemley showed that under pressure, sulfur becomes an elemental superconductor, making it an ideal material for studying the basic physics of superconductivity.  

Now, experiments with compressed sulfur have shown there is a novel intermediate state — a so-called bosonic insulator — before superconducting properties appear. 

A paper in Proceedings of the National Academy of Sciences led by postdoctoral researcher Kui Wang documents this surprising behavior. Wang and Hemley, in collaboration with researchers at Jilin University in China, subjected sulfur to high pressures, low temperatures and strong magnetic fields. Their study demonstrated how applying pressure to materials can uncover hidden states of matter and physical behavior. 

Experiments revealed the bosonic insulator state as the material cooled. Just before the compressed sulfur reached the critical temperature where electrical resistance dropped to zero, the resistance instead sharply increased. The results reflect a transition where the material changes from behaving like a metal to behaving like an insulator before becoming a superconductor. 

“This is the first instance of the concurrent observation of a prominent resistance peak as a function of temperature, magnetic field and current in the same superconductor,” Wang said. 

It’s also the first time this behavior has been found in a pure, three-dimensional elemental superconductor without additional elements or impurities. As such, it offers a simple system for researchers to strip away extraneous effects and focus on fundamental principles. 

“The study shows that complicating factors that have been invoked previously to explain related observations in complex materials are not needed,” Wang said. 

The discovery is a stepping stone toward solving complex problems in condensed matter physics, paving the way for innovations in quantum computing, efficient power transmission and advanced materials design. 

“This work unveils new, poorly understood physics associated with the transitions of materials into superconducting states,” said Hemley, Liberal Arts and Sciences Distinguished Chair in the Natural Sciences. “The discovery highlights how subjecting materials to high pressure can lead to the discovery of not only new materials but also new physical phenomena.”