Promotions and Appointments Effective July 1, 2017

Kaustubh Agashe, who was promoted to the rank of Professor, is a particle theorist who was recently named a Fermilab Distinguished Scholar. Dr. Agashe researches mathematical extensions to the Standard Model, making theoretical predictions that can be tested experimentally in settings including the Large Hadron Collider and future accelerator facilities.


Carter Hall, who was promoted to the rank of Professor, researches neutrinos and dark matter. He has worked on the Enriched Xenon Observatory (EXO-200), and the Large Underground Xenon (LUX) detector, and is the new spokesperson for the LZ Dark Matter Experiment, based in the Sanford Underground Research Facility in the former Homestead gold mine in South Dakota.


Peter Shawhan, who was promoted to the rank of Professor, works on the LIGO experiment based in Louisiana and in Washington state. In recent years, LIGO made major news by confirming the existence of gravitational waves and thereby validating Einstein’s theory of relativity. Prof. Shawhan is also the Chair of the American Physical Society’s Division of Gravitational Physics.


Sylvester James “Jim” Gates Jr. has been appointed a College Park Professor. Gates joined the UMD faculty in 1984, and in the ensuing decades became an internationally-known advocate of science education. He is a member of the National Academy of Sciences and a recipient of the National Medal of Science. He is now the Co-Director of the Presidential Scholars Program at Brown University.


David Clarke was promoted to the rank of Assistant Research Scientist. He received his Ph.D. at Johns Hopkins University, and his research focuses on the design, analysis, and manipulation of topological phases of matter for applications in quantum information processing.


Cornelius Griggs was promoted to the rank of Assistant Research Scientist. He received his Ph.D. at the University of Notre Dame, and works on advancing the techniques of superconducting gravity gradiometry and its applications, such as earlier detection of earthquakes.


Greg Jenkins was promoted to the rank of Associate Research Scientist. He received his Ph.D. at the University of Maryland, and studies the magneto-optical studies of Dirac and Weyl semimetals.


Hyunsoo Kim was promoted to the rank of Assistant Research Scientist. Kim received his Ph.D. at Iowa State University, and works in the development and application of very low-temperature instrumentation for the study of the electronic properties of novel materials.


Norbert Linke was promoted to the rank of Assistant Research Scientist. Dr. Linke received his Ph.D. at the University of Oxford, and at UMD was part of the team that realized the first programmable quantum computer based on five Ytterbium ions.

Atomic cousins team up in early quantum networking node

Large-scale quantum computers, which are an active pursuit of many university labs and tech giants, remain years away. But that hasn’t stopped some scientists from thinking ahead, to a time when quantum computers might be linked together in a network or a single quantum computer might be split up across many interconnected nodes.

Read more.

Read more

New Members of the Department of Physics

Four assistant professors have recently joined UMD Physics.

Maissam Barkeshli received his Ph.D. from the Massachusetts Institute of Technology. Afterward, he was a Simons Postdoctoral Fellow at Stanford University and a postdoctoral researcher at Microsoft's Station Q at UC Santa Barbara. He works on several topics in complex quantum many-body phenomena and is a member of the Condensed Matter Theory Center and Joint Quantum Institute.  

Brian Swingle received his Ph.D. from the Massachusetts Institute of Technology, and held postdoctoral positions at Harvard University, the It from Qubit Simons Collaboration and Stanford University. He researches quantum information and is a member of the Condensed Matter Theory Center, the Joint Center for Quantum Information and Computer Science and the Maryland Center for Fundamental Physics.

Zohreh Davoudi received her Ph.D. at the University of Washington and recently completed a postdoctoral appointment at the Massachusetts Institute of Technology. She studies strongly-interacting systems of hadrons and nuclei, using analytical and computational methods such as effective field theories and lattice quantum chromodynamics. She will be a member of the Maryland Center for Fundamental Physics and hold a joint appointment at Brookhaven National Lab through the Riken Fellowship program.

Anson Hook will begin in the spring semester of 2018, after completing a postdoctoral appointment at Stanford University, where he received his Ph.D. in 2012. He has also held a postdoctoral appointment at the Institute for Advanced Studies. Hook researches the extent to which exotic field theory phenomena can be used to solve existing problems in particle physics. He will be a member of the Maryland Center for Fundamental Physics.

In addition, two members of the Department of Engineering and the Institute for Research in Electronics and Applied Physics (IREAP) now hold appointments in Physics.

Associate Professor Mohammad Hafezi received his Ph.D. at Harvard University. His interests include the theoretical and experimental investigation of strongly-correlated systems and topological physics, nanophotonics and optomechanics, and hybrid quantum systems. He is a Fellow of the Joint Quantum Institute.

Professor Edo Waks received his Ph.D. in Electrical Engineering from Stanford University. He researches nanoscale photonic and semiconductor devices for applications in quantum computation, communication, and sensing. He is a Fellow of the Joint Quantum Institute.

Tiny magnetic tremors unlock exotic superconductivity

tiny magneticArtistic rendering of exotic 2D superconductivity in a material made from nanolayers of nickel (bottom layer) and bismuth (top layer). Magnetic fluctuations from the nickel layer allow electrons to pair up on the surface of bismuth. These pairs move losslessly in a phenomenon called superconductivity. (Credit E. Edwards; transmission electron microscopy images from the real materials are projected onto the cube layers. These images were re-used for this graphic with author permission)

Deep within solids, individual electrons zip around on a nanoscale highway paved with atoms. For the most part, these electrons avoid one another, kept in separate lanes by their mutual repulsion. But vibrations in the atomic road can blur their lanes and sometimes allow the tiny particles to pair up. The result is smooth and lossless travel, and it’s one way to create superconductivity.

But there are other, less common ways to achieve this effect. Scientists from the University of Maryland (UMD), the University of California, Irvine (UCI) and Fudan University have now shown that tiny magnetic tremors lead to superconductivity in a material made from metallic nano-layers. And, beyond that, the resulting electron pairs shatter a fundamental symmetry between past and future. Although the material is a known superconductor, these researchers provide a theoretical model and measurement, which, for the first time, unambiguously reveals the material’s exotic nature.

In quantum materials, breaking the symmetry between the past and the future often signifies unconventional phases of matter. The nickel-bismuth (Ni-Bi) sample studied here is the first example of a 2D material where this type of superconductivity is intrinsic, meaning that it happens without the help of external agents, such as a nearby superconductor. These findings, recently published in Science Advances, make Ni-Bi an appealing choice for use in future quantum computers. This research may also assist scientists in their search for other similarly strange superconductors.

Mehdi Kargarian*, a postdoctoral researcher at UMD and a co-author of the paper, explains that even after a century of study, superconductivity remains a vibrant area of research. “It is a rather old problem, so it is surprising that people are still discovering types of superconductivity in the lab that are unprecedented,” Kargarian says, adding that there are typically two questions scientists ask of a new superconductor. “First, we want to understand the underlying electron pairing—what is causing the superconductivity,” he says. “The second thing, related to applications, is to see if superconductivity is possible at higher temperatures.”

Superconductors, particularly the exotic types, largely remain shackled to unwieldy cryogenic equipment. Scientists are searching for ways to push superconducting temperatures higher, thus making these materials easier to use for things like improved electricity distribution and building quantum devices. In this new research, the team tackles Kargarian’s first question and the material hints at a positive outlook for the second question. Its exotic superconductivity, although still cryogenic, occurs at a higher temperature compared to other similar systems.

Ni-Bi superconductivity was first observed in the early 1990s. But later, when Fudan University scientists published studies of an ultrapure, ultra-thin sample, they noticed something unusual happening.

The strangeness starts with the superconductivity itself. Bismuth alone is not a superconductor, except under extraordinarily low temperatures and high pressure—conditions that are not easy to achieve. Nickel is magnetic and not a superconductor. In fact, strong magnets are known to suppress the effect. This means that too much nickel destroys the superconductivity, but a small amount induces it.

UMD theorists* proposed that fluctuations in nickel’s magnetism are at the heart of this peculiar effect. These tiny magnetic tremors help electrons to form pairs, thus doing the work performed by vibrations in conventional superconductors. If there is too much nickel, magnetism dominates and the effect of the fluctuations diminishes. If there is too much bismuth, then the top surface, where superconductivity takes place, is too far away from the source of magnetic fluctuations.

The goldilocks zone occurs when a twenty-nanometer-thick bismuth layer is grown on top of two nanometers of nickel. For this layer combination, superconductivity happens at around 4 degrees above absolute zero. While this is about as cold as deep space, it is actually quite lab-friendly and reachable using standard cryogenic equipment.

The idea that magnetic fluctuations can promote superconductivity is not new and dates back to the end of the 20th century. However, most earlier examples of such behavior require strict operating conditions, such as high pressure. The researchers explain that Ni-Bi is different because straightforward cooling is enough to achieve this type of exotic superconductivity, which breaks time symmetry.

The researchers employed a highly customized apparatus to search for signs of the broken symmetry. Light should rotate when reflected from samples that have this property. For Ni-Bi, the expected amount of light rotation is tens of nanoradians, which is about 100 billionths of a tick on a watch face. Jing Xia*, a co-author of the paper and a professor at UCI, has one of the only devices in the world capable of measuring such an imperceptible light rotation.

In order to measure this rotation for Ni-Bi, light waves are first injected into one end of a single special-purpose optical fiber. The two waves travel through the fiber, as if on independent paths. They hit the sample and then retrace their paths. Upon return, the waves are combined and form a pattern. Rotations of the light waves—from, say, symmetry breaking—will show up in the analyzed pattern as small translations. Xia and his colleagues at UCI measured around 100 nanoradians of rotation, confirming the broken symmetry. Importantly, the effect appeared just as the Ni-Bi sample became a superconductor, suggesting that the broken time symmetry and the appearance of superconductivity are strongly linked.

This form of superconductivity is rare and researchers say that there is still no recipe for making it happen. But, as Xia points out, there is guidance in the math behind the electron behavior. “We know mathematically how to make electron pairs break time-reversal symmetry,” Xia says. Practically, how do you achieve this formulaically? That is the million-dollar question. But my instinct is that when you do get magnetic fluctuation-mediated superconductivity, like in this material, then it is highly likely you get break that symmetry.”

* M. Kargarian is a postdoctoral researcher at the Condensed Matter Theory Center (CMTC), University of Maryland (UMD) and is affiliated with the Joint Quantum Institute. V. Yakovenko and V. Galitski are members of CMTC, fellows of the Joint Quantum Institute, and UMD professors. J. Xia is a professor at the University of California, Irvine.

Written by E. Edwards/JQI

REFERENCE PUBLICATION
"Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers," X. Gong, M. Kargarian, A. Stern, D. Yue, H. Zhou, X. Jin, V.M. Galitski, V.M. Yakovenko, J. Xia, Science Advances, 3, (2017)

RELATED JQI ARTICLES

Topological Superconductors

Tiny tug unleashes cryogenic currents