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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.”

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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.

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An international team of scientists has discovered an exotic new form of topological state in a large class of 3D semi-metallic crystals called Dirac semimetals. The researchers developed extensive mathematical machinery to bridge the gap between theoretical models with forms of “higher-order” topology (topology that manifests only at the boundary of a boundary) and the physical behavior of electrons in real materials.

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A Majorana particle is a fermion that is its own anti-particle. Majorana particles were postulated to exist by Ettore Majorana in a now famous paper written in 1937. However, such particles have not  been discovered in nature to date.  The possible realization of Majorana particles in condensed matter systems has generated much excitement and revived interest in observing these particles, especially because the condensed matter realization may be useful for topological quantum computation. A new paper by Illinois Physics Professor Vidya Madhavan and collaborators recently published in Science shows the first evidence for propagating 1D Majorana modes realized at 1D domain walls in a superconductor  FeSexTe1−x

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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.

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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.

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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.

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Illinois Physics Professor Philip Phillips and Math Professor Gabriele La Nave have theorized a new kind of electromagnetism far beyond anything conceivable in classical electromagnetism today, a conjecture that would upend our current understanding of the physical world, from the propagation of light to the quantization of charge. Their revolutionary new theory, which Phillips has dubbed “fractional electromagnetism,” would also solve an intriguing problem that has baffled physicists for decades, elucidating emergent behavior in the “strange metal” of the cuprate superconductors.

This research is published in an upcoming colloquium paper in Reviews of Modern Physics (arXiv:1904.01023v1).

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Researchers at the Paul Scherrer Institute in Switzerland working with scientists at institutions in Germany, Great Britain, Spain, and the US, have investigated a novel crystalline material, a chiral semimetal, exhibiting never-before-seen electronic properties. These include so-called chiral Rarita-Schwinger fermions in the interior and very long, quadruple topological Fermi arcs on the surface. The crystal, synthesized at the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany, comprises aluminum and platinum atoms arranged in a helical pattern, like a spiral staircase. It’s the crystal’s chiral symmetry that hosts exotic emergent electronic properties.

These research findings, published online in the journal Nature Physics on May 6, 2019, validate a 2016 theoretical prediction by University of Illinois Physics Professor Barry Bradlyn (then a postdoc at the Princeton Center for Theoretical Science), et al., in the journal Science (vol. 353, no. 6299, aaf5037). That theoretical work was subsequently rounded out by a team of physicists at Princeton University, in research published in 2017 and 2018.

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University of Illinois at Urbana-Champaign Emeritus and Research Professor of Physics Tai-Chang Chiang has been selected for the 2019 Arthur H. Compton Award of the Advanced Photon Source Users Organization (APSUO). The award recognizes a significant scientific or technical accomplishment at the Advanced Photon Source (APS), a national synchrotron-radiation light source research facility housed at Argonne National Laboratory and funded by the US Department of Energy’s Office of Science. The award will be presented to Chiang at the APS/CNM User Meeting in early May.

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Professor Nadya Mason has been elected a Fellow of the American Physical Society (APS) "for seminal contributions to the understanding of electronic transport in low dimensional conductors, mesoscopic superconducting systems, and topological quantum materials."

Mason is an experimental condensed matter physicist who has earned a reputation for her deep-sighted and thorough lines of attack on the most pressing problems in strongly correlated nanoscale physics.

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Recently, a team of scientists led by Pablo Jarillo-Herrero at the Massachusetts Institute of Technology (MIT) created a huge stir in the field of condensed matter physics when they showed that two sheets of graphene twisted at specific angles—dubbed “magic-angle” graphene—display two emergent phases of matter not observed in single sheets of graphene. Graphene is a honeycomb lattice of carbon atoms—it’s essentially a one-atom-thick layer of graphite, the dark, flaky material in pencils. 

Researchers at the University of Illinois at Urbana-Champaign have recently shown that the insulating behavior reported by the MIT team has been misattributed. Professor Philip Phillips, a noted expert in the physics of Mott insulators, says a careful review of the MIT experimental data by his team revealed that the insulating behavior of the “magic-angle” graphene is not Mott insulation, but something even more profounda Wigner crystal.

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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.

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Researchers have produced a “human scale” demonstration of a new phase of matter called quadrupole topological insulators that was recently predicted using theoretical physics. These are the first experimental findings to validate this theory.

The researchers report their findings in the journal Nature.

The team’s work with QTIs was born out of the decade-old understanding of the properties of a class of materials called topological insulators. “TIs are electrical insulators on the inside and conductors along their boundaries, and may hold great potential for helping build low-power, robust computers and devices, all defined at the atomic scale,” said mechanical science and engineering professor and senior investigator Gaurav Bahl.

The uncommon properties of TIs make them a special form of electronic matter. “Collections of electrons can form their own phases within materials. These can be familiar solid, liquid and gas phases like water, but they can also sometimes form more unusual phases like a TI,” said co-author and physics professor Taylor Hughes.

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On Thursdays throughout the semester, staff writer Adalberto Toledo will book an appointment with a UI professor. Today: physics professor NADYA MASON, director of the new Materials Research Science and Engineering Center.