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Researchers at the University of Illinois at Urbana-Champaign and Princeton University have theoretically predicted a new class of insulating phases of matter in crystalline materials, pinpointed where they might be found in nature, and in the process generalized the fundamental quantum theory of Berry phases in solid state systems. What’s more, these insulators generate electric quadrupole or octupole moments—which can be thought of roughly as very specific electric fields—that are quantized. Quantized observables are a gold standard in condensed matter research, because experimental results that measure these observables have to, in principle, exactly match theoretical predictions—leaving no wiggle room for doubt, even in highly complex systems.

The research, which is the combined effort of graduate student Wladimir Benalcazar and Associate Professor of Physics Taylor Hughes of the Institute for Condensed Matter Theory at the U. of I., and Professor of Physics B. Andrei Bernevig of Princeton, is published in the July 7, 2017 issue of the journal Science.

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Since the discovery two decades ago of the unconventional topological superconductor Sr2RuO4, scientists have extensively investigated its properties at temperatures below its 1 K critical temperature (Tc), at which a phase transition from a metal to a superconducting state occurs. Now experiments done at the University of Illinois at Urbana-Champaign in the Madhavan and Abbamonte laboratories, in collaboration with researchers at six institutions in the U.S., Canada, United Kingdom, and Japan, have shed new light on the electronic properties of this material at temperatures 4 K above Tc. The team’s findings may elucidate yet-unresolved questions about Sr2RuO4’s emergent properties in the superconducting state.

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In a surprising new discovery, alpha-tin, commonly called gray tin, exhibits a novel electronic phase when its crystal structure is strained, putting it in a rare new class of 3D materials called topological Dirac semimetals (TDSs). Only two other TDS materials are known to exist, discovered as recently as 2013. Alpha-tin now joins this class as its only simple-element member.

This discovery holds promise for novel physics and many potential applications in technology. The findings are the work of Caizhi Xu, a physics graduate student at the University of Illinois at Urbana-Champaign, working under U. of I. Professor Tai-Chang Chiang and in collaboration with scientists at the Advanced Light Source at the Lawrence Berkeley National Laboratory and six other institutions internationally.

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Topological insulators, an exciting, relatively new class of materials, are capable of carrying electricity along the edge of the surface, while the bulk of the material acts as an electrical insulator. Practical applications for these materials are still mostly a matter of theory, as scientists probe their microscopic properties to better understand the fundamental physics that govern their peculiar behavior.

Using atomic quantum-simulation, an experimental technique involving finely tuned lasers and ultracold atoms about a billion times colder than room temperature, to replicate the properties of a topological insulator, a team of researchers at the University of Illinois at Urbana-Champaign has directly observed for the first time the protected boundary state (the topological soliton state) of the topological insulator trans-polyacetylene. The transport properties of this organic polymer are typical of topological insulators and of the Su-Schrieffer-Heeger (SSH) model.

Physics graduate students Eric Meier and Fangzhao Alex An, working with Professor Bryce Gadway, developed a new experimental method, an engineered approach that allows the team to probe quantum transport phenomena.

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The other half of the Nobel prize, awarded for “topological phase transitions,” also unites topology and physics, but “topology enters in a somewhat different way,” says Eduardo Fradkin, a physicist at the University of Illinois Urbana-Champaign. 

Relevant here is the fact that topological properties often cannot be determined locally. An ant sitting on a pastry can’t tell by looking around whether the perch is a bun, bagel, or pretzel.

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Physics professor Taylor Hughes and mechanical science and engineering professor Gaurav Bahl of the University of Illinois at Urbana-Champaign are part of an interdisciplinary team that will study non-reversible sound wave propagation over the next four years, with a range of promising potential applications.

The National Science Foundation has announced a $2-million research award to the team, which includes University of Oregon physics professor Hailin Wang and Duke University electrical and computer engineering professor Steven Cummer. The grant is part of a broader $18-million NSF-funded initiative, the Emerging Frontiers in Research and Innovation (EFRI) program, supporting nine teams—a total of 37 researchers at 17 institutions—to pursue fundamental research in the area of new light and acoustic wave propagation, known as NewLAW.

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Experimenters have approximated the Leggett and Garg test. In 2011, White and colleagues demonstrated the extrastrong correlations in quantum optics, although in an average way and not with a single photon. Now, Joseph Formaggio, a neutrino physicist at the Massachusetts Institute of Technology in Cambridge, and colleagues provide a demonstration using data from the Main Injector Neutrino Oscillation Search (MINOS) experiment at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, which fires neutrinos at near-light-speed 735 kilometers to a 5.4-kiloton detector in the Soudan Mine in Minnesota.

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Emeritus and Research Professor Tai-Chang Chiang of the University of Illinois at Urbana-Champaign has been elected by the Academia Sinica to its 2016 class of Academicians. He is among 22 scholars across all academic disciplines to receive this high honor this year. Academia Sinica is the national academy of Taiwan. Former Academicians in the mathematics and physics division include Nobel laureates T.D. Lee, C.N. Yang, Sam Ting, and Daniel Tsui.

Over the course of his career, Chiang has made lasting contributions to condensed matter physics, surface science, and synchrotron radiation research, including several truly groundbreaking findings. He has authored about 300 journal articles, and his work has been cited more than 8,500 times.

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  • Condensed Matter Physics

Professor Dale Van Harlingen, head of the Department of Physics at the University of Illinois at Urbana-Champaign, has been selected to receive a Campus Executive Officer Distinguished Leadership Award by the Office of the Provost. The award recognizes exceptional academic leadership and vision by an executive officer within a college or campus unit.

The tenth head in the department’s 126-year history, Van Harlingen took on the unit’s top administrative role in 2006. His first years were tumultuous ones for the University, marked by abrupt changes in campus leadership and tremendous budgetary challenges. Guiding the department through this period, Van Harlingen sought ways to enhance the department’s productivity and impact through initiatives that would improve research infrastructure, teaching spaces, and strategic hiring of faculty and support staff.

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Now, two teams at the University of Illinois at Urbana Champaign, working together and attacking the problem from different physics disciplines, have shed new light on our understanding of disordered quantum materials. Professor Brian DeMarco and his group perform innovative experiments in atomic, molecular, and optical physics using ultracold atoms trapped in an optical lattice to simulate phenomena in solid materials. Professor David Ceperley and his group work in theoretical condensed matter physics; they perform supercomputing simulations to model phenomena in solid materials.

The two groups collaborated across physics disciplines to understand how disorder in a quantum material gives rise to an exotic quantum state called a Bose glass. The results are published in Nature Physics in the article, “Probing the Bose glass–superfluid transition using quantum quenches of disorder.”

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What’s exciting to you about working in this field? One thing is that it’s a new field. And because it involves “weakly correlated” physics, we can actually hope to make precise calculations about what is going to happen in experiments. It’s just a matter of asking the right question. That, to me, lends itself to more creativity, in a way that I feel can be rewarding. Whereas, if I came up with a new theory of high-temperature superconductivity, nobody would believe it but me.

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Researchers working to create next-generation electronic systems and to understand the fundamental properties of magnetism and electronics to tackle grand challenges such as quantum computing have a new cutting-edge tool in their arsenal. The Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility located at Argonne National Laboratory, recently unveiled a new capability: the Intermediate Energy X-ray (IEX) beamline at sector 29.

Using relatively low-energy X-rays, the IEX beamline at the APS will help illuminate electronic ordering and emergent phenomena in ordered materials to better understand the origins of distinct electronic properties. Another important feature for users is a greater ability to adjust X-ray parameters to meet experimental needs.

Currently in commissioning phase, the IEX beamline begins its first user runs in January 2016. With its state-of-the-art electromagnetic insertion device, highly adaptive X-ray optics, and compatible endstation techniques for X-ray photoelectron spectroscopy and scattering, it opens a new era for X-ray research in sciences ranging from condensed matter physics and materials science to molecular chemistry.

Read more at: http://phys.org/news/2015-11-intermediate-energy-x-ray-beamline.html#jCp

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How does transitional turbulence die away? And what controls its lifetime? These questions have perplexed scientists ever since the first experiments were performed in 1883.

Now, physicist Nigel Goldenfeld, graduate student Hong-Yan Shih, and former undergraduate student Tsung-Lin Hsieh at tthe University of Illinois at Urbana-Champaign have developed a theoretical understanding of this laminar-turbulent transition that explains the lifetime of turbulent flows.

“What my colleagues and I found is a completely unexpected analogy between the transition to turbulent flow and the behavior of an ecosystem on the edge of extinction," Goldenfeld remarks.

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Apparently, size doesn't always matter. An extensive study by an interdisciplinary research group suggests that the deformation properties of nanocrystals are not much different from those of the Earth's crust.

"When solid materials such as nanocrystals, bulk metallic glasses, rocks, or granular materials are slowly deformed by compression or shear, they slip intermittently with slip-avalanches similar to earthquakes," explained Karin Dahmen, a professor of physics at the University of Illinois at Urbana-Champaign. "Typically these systems are studied separately. But we found that the scaling behavior of their slip statistics agree across a surprisingly wide range of different length scales and material structures."

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  • Condensed Matter Physics

An ultrapure material taken to pressures greater than that in the depths of the ocean and chilled to temperatures colder than outer space has revealed an unexpected phase transition that crosses two different phase categories.

A Purdue University-led team of researchers observed electrons transition from a topologically ordered phase to a broken symmetry phase, as predicted by University of Illinois theoretical condensed matter physicist, Eduardo Fradkin.