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There are times when superconductors—materials through which electric current can travel without resistance and thus without losing energy—don’t live up to their reputation. Nadya Mason of the University of Illinois at Urbana-Champaign has been making strides toward understanding when and how electron energy loss, or dissipation, arises in otherwise superconducting systems. She had planned to share this work in the Edward A. Bouchet Award Talk at the March Meeting of the American Physical Society earlier this month. (The meeting was canceled due to concerns about the new coronavirus disease, COVID-19, but Physics is reporting on some of the results that would have been presented.)

Modern technology is largely based on normal conductors, but electrical currents in these materials always dissipate some energy as heat. “Superconductors give us a great opportunity to save energy by reducing dissipation,” Mason says. “But in order to use superconductors, we have to understand how dissipation affects them in particular, and how to minimize [dissipation] and control it.”

Two University of Illinois at Urbana-Champaign scientists are among 126 recipients of the 2020 Sloan Research Fellowships from the Alfred P. Sloan Foundation. This honor is one of the most competitive and prestigious awards available to early career researchers. 

This year’s Illinois recipients are physics professor Barry Bradlyn and electrical and computer engineering professor Zhizhen Zhao.

Scientists at the Max Planck Institute for Chemical Physics of Solids in Dresden, Princeton University, the University of Illinois at Urbana-Champaign, and the University of the Chinese Academy of Sciences have spotted the fingerprint of an elusive particle: The axion—first predicted 42 years ago as an elementary particle in extensions of the standard model of particle physics. Based on predictions from Illinois Physics Professor Barry Bradlyn and Princeton Physics Professor Andrei Bernevig's group, the group of Chemical Physics Professor Claudia Felser at Max Planck in Dresden produced the charge density wave Weyl metalloid (TaSe₄)₂I and investigated the electrical conduction in this material under the influence of electric and magnetic fields. It was found that the electric current in this material below -11 °C is actually carried by axion particles.

Physics Professor Smitha Vishveshwara has been elected a Fellow of the American Physical Society (APS) “for pioneering theory of quantum dynamics in nonequilibrium systems and novel phenomena in cold Bose gases.”

Vishveshwara is a theoretical condensed matter physicist with broad research interests in non-equilibrium and strongly correlated systems at all scales, from subatomic to cosmic. A common thread throughout her work is the characterization of emergent phenomena in quantum states of matter—including superconductivity, superfluidity, Mott insulators, topological systems, fractional quantum Hall states, and Majorana wires. In true “Urbana style,” Vishveshwara’s collaborations at Illinois and beyond, often involving close rapport with experimental colleagues, have produced viable experimental stratagems and identified clear signatures that characterize particular states of matter.

One of the greatest mysteries in condensed matter physics is the exact relationship between charge order and superconductivity in cuprate superconductors. In superconductors, electrons move freely through the material—there is zero resistance when it’s cooled below its critical temperature. However, the cuprates simultaneously exhibit superconductivity and charge order in patterns of alternating stripes. This is paradoxical in that charge order describes areas of confined electrons. How can superconductivity and charge order coexist?  

Now researchers at the University of Illinois at Urbana-Champaign, collaborating with scientists at the SLAC National Accelerator Laboratory, have shed new light on how these disparate states can exist adjacent to one another. Illinois Physics post-doctoral researcher Matteo Mitrano, Professor Peter Abbamonte, and their team applied a new x-ray scattering technique, time-resolved resonant soft x-ray scattering, taking advantage of the state-of-the-art equipment at SLAC. This method enabled the scientists to probe the striped charge order phase with an unprecedented energy resolution. This is the first time this has been done at an energy scale relevant to superconductivity.

Now, a novel sample-growing technique developed at the U. of I. has overcome these obstacles. Developed by physics professor James Eckstein in collaboration with physics professor Tai-Chang Chiang, the new “flip-chip” TI/SC sample-growing technique allowed the scientists to produce layered thin-films of the well-studied TI bismuth selenide on top of the prototypical SC niobium—despite their incompatible crystalline lattice structures and the highly reactive nature of niobium.

These two materials taken together are ideal for probing fundamental aspects of the TI/SC physics, according to Chiang: “This is arguably the simplest example of a TI/SC in terms of the electronic and chemical structures. And the SC we used has the highest transition temperature among all elements in the periodic table, which makes the physics more accessible. This is really ideal; it provides a simpler, more accessible basis for exploring the basics of topological superconductivity,” Chiang comments.