How do magnets work?
Laura H. Greene received her BS and MS degrees from The Ohio State University and in 1984, received a Ph.D. in Physics from Cornell University, investigating the linear and non-linear far-infrared properties of materials. She joined Bell Laboratories and then Bellcore, where she researched thin-film growth and tunneling of metallic multilayers, heavy-Fermions, superconductor-semiconductor hybrid structures and high-temperature superconductors. In 1992, she joined the senior physics faculty at the University of Illinois at Urbana-Champaign.
Her research continues in experimental condensed matter physics focusing on highly-correlated electron systems and novel materials; in particular high-temperature superconductors, and the interfaces between metallic superconductors and compound-semiconductor heterostructures. Thin film and multilayer growth with extensive materials analysis is routinely performed. Planar tunneling spectroscopy, electronic transport, Raman scattering, electron spin resonance and muon spin relaxation are employed to investigate mechanisms of superconductivity and charge and transport across superconducting interfaces. Much of her research investigates the role of broken symmetries and their physical ramifications in condensed matter systems, especially that of spontaneously broken-time reversal symmetry in unconventional superconductors.
Greene has served the American Physical Society as a General Councilor, member of their Executive Board, member of their Division of Condensed Matter Physics Nominating Committee and Chair of their Committee on Committees. She was elected as a delegate to the Low-Temperature Physics Commission of the International Union of Pure and Applied Physics, where she also serves on their US Liaison Committee. She is a founding member or the Board of Trustees of the Los Alamos-based Institute for Complex and Adaptive Materials. In 1999, Greene was elected to member-at-large of the Council of Gordon Research Conferences and serves on their Schedule and Selection Committee. In 2000, Greene was elected to the Electorate Nominating Committee of the Physics Section of the American Association of the Advancement of Science. Also in 2000, she was appointed by the Secretary of Energy, Bill Richardson, to the Basic Energy Sciences Advisory Committee (BESAC) of the Department of Energy. She is a Fellow of the American Physical Society, the American Association for the Advancement of Science, the American Academy of Arts and Sciences, and the National Academy of Sciences. In 1994, Greene was the recipient of the Maria Goeppert-Mayer Award of the American Physical Society. In 1999, she received the E. O. Lawrence Award for Materials Research from the Department of Energy. In 2000, she was named to the Swanlund Endowed Chair of the University of Illinois. Over her career, Greene has co-authored approximately 140 publications and has presented more than 180 invited talks.
Our main research efforts are directed towards understanding the physics of highly correlated electron materials, focusing on superconductors. In particular, we study how electrons cross superconducting interfaces with a powerful technique known as tunneling spectroscopy. These measurements are mostly performed on thin films of low-temperature and high-temperature superconductors that we grow in our own laboratory. In our studies of low-temperature superconductors, we have found novel ways to study electronic transport across the superconductor-semiconductor interface. In our studies of high-temperature superconductors, we have found that tunneling spectroscopy can be used to probe symmetries that are broken in nature, and recently discovered a superconducting state a that breaks time-reversal symmetry.
Superconductive Tunneling Spectroscopy and Electronic Transport in Pure and Doped YBa2Cu3O7
Thin Films Reliable film growth, electronic transport, magnetization measurements, and superconductive tunneling provide the foundation for our investigations into the electronic properties of high-temperature superconductors. Thin films of pure and doped YBa2Cu3O7 are grown by sputter deposition. These thin films are also grown in various crystallographic orientations, allowing charge transport measurements along different lattice directions in this highly anisotropic material. Information on the interface properties is being provided through these measurements. Furthermore, tunneling provides a powerful spectroscopy of the superconducting state, which will help elucidate the mechanism of high-temperature superconductivity.
Reliable Planar Tunnel Junction Fabrication with Self-assembled Monolayers
To date, the most reliable method of tunnel junction fabrication on high-temperature superconductors has been by evaporation of Pb counter electrodes directly on the YBa2Cu3O7 surface. A chemical interaction between these materials causes a reproducible, insulating tunnel barrier, but also a ~30 Å thick damage layer. To avoid such surface degradation, we are investigating self-assembled monolayers as the tunneling barrier material. The surface of YBa2Cu3O7 thin films are chemically modified with, for example, an alkylamines insulating layer. Resulting tunnel junctions are reliable and have provided intriguing new spectroscopic data indicating the existence of nonconventional order parameters.
Tunneling Spectroscopy of High-Temperature Superconductors
We take advantage of the unconventional nature of high-temperature superconductors to probe details of the superconducting and normal-state properties. Tunneling spectroscopic studies of the surface-induced Andreev bound state (ABS) are performed. This (ABS) is a bound-state of quasi-electrons and quasi-holes that form near to the interface of an unconventional superconductor, such as the d-wave superconductor, YBa2Cu3O7 . We investigate this ABS as a function of several physical parameters, including high-magnetic field and disorder in other unconventional superconductors.
Charge Transport across Superconductor-Semiconductor and Superconductor–Normal-Metal Interfaces
This research program is a coordinated experimental and theoretical study of the static and dynamic properties of hybrid superconductor-semiconductor structures. Electronic transport, superconductive tunneling, magnetization, and light-scattering measurements are conducted on planar, microfabricated structures of high-quality Nb and NbNx thin films grown directly on III-V semiconductor heterostructures. Details of the superconducting proximity effect, Andreev reflection, and tunneling are investigated. We have performed the first optical detection of the superconducting proximity effect: Raman spectroscopy is the optical probe of an InAs interface in good electrical contact with a superconductor.
Charge and Spin Transport at the Interface of Unconventional Superconductors
Quasi-electrons and quasi-holes travel in a dissipationless current along the surface of an unconventional superconductor. At low temperatures, these currents move spontaneously, signifying a state with broken time reversal symmetry. We study the electrodynamics of these Andreev bound state currents by several transport and optical methods.
• Number of Citations: 7,120; Average Citations per Item: 55.19; h-index: 38
• In The Thompson ISI’s 1120 Most Cited Physicist, 1981 – 1997, where physicists are ranked in this time period by the total number of citations. Rank = # 182; Rank by citations per paper (impact) = # 18.
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