Laura H Greene

For More Information

• Greene Group
• Vodcast of Professor Greene describing her scientific career
• Laura Greene's Curriculum Vitae

Education

• Ph.D., Physics, Cornell University, 1984

Biography

Laura H. Greene is a Swanlund and Center for Advanced Study Professor of Physics at the University of Illinois at Urbana-Champaign and Associate Director for the Center for Emergent Superconductivity. She received her BS from Ohio State, worked at Hughes Aircraft, and then received her PhD in 1984 from Cornell. After nine years at Bell Labs and subsequently Bellcore, she joined the Physics faculty at Illinois. Greene's research is in experimental condensed matter physics investigating strongly correlated electron systems. Much of her research focuses on fundamental studies to determine the mechanisms of unconventional superconductivity by planar tunneling and point contact electron spectroscopies, and on developing methods for predictive design of new families of superconducting materials. In the quest for these long-term goals, spectroscopic studies of the electronic structure of heavy fermions, unconventional superconductors, and other novel materials that show strong electronic correlations are performed. Studies of superconducting proximity effects on novel normal-state and superconducting materials are also done. Another long-term goal is in improving the current carrying capabilities of high-temperature superconductors for impacting a variety of applications, with a focus on those impacting superconductivity for energy storage, production, and transmission.

Research Statement

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 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.

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Selected Articles in Journals

• L. H. Greene. Deciphering Electron Matter in Novel Superconductors. ASP News Back Page (Op-Ed commissioned by the American Physical Society, to be published in 2016).
• A.V. Burmistrova, I.A. Devayatov, Alexander A. Golubov, Keihi Yada, Yukio Tanaka, M. Tortello, R.S. Gonnelli, V. A. Stephanov, X. Ding, H.-H. Wen, L.H. Greene. Josephson current in Fe-based superconducting junctions: Theory and experiment. Phys. Rev. B 91, 214501 (2015).
• S. Narasiwodeyar, M. Dwyer, M. Liu, W. K. Park, and L. H. Greene. Two-step fabrication technique of gold tips for use in point-contact spectroscopy. Rev. Sci. Instrum. 86, 033903 (2015).
• W.-C. Lee, W. K. Park, H. Z. Arham, L. H. Greene, and P. W. Phillips. Theory of point contact spectroscopy in correlated electron materials. Proc. Natl. Acad. Sci. 112, 651-656 (2015).
• H. Hu, J.-H. Kwon, M. Zheng, C. Zhang, L. H. Greene, J. N. Eckstein, J.-M. Zuo. Impact of interstitial oxygen on the electronic and magnetic structure in superconducting Fe_1+yTeO_x thin films. Phys. Rev. B 90, 180504(R), 2014.
• W.K. Park, S.M. Narasiwodeyar, E.D. Bauer, P.H. Tobash, R.E. Baumbach, F. Ronning, J.L. Sarrao, J.D. Thompson, and L.H. Greene. Hidden order and hybridization gap in URu₂Si₂ via quasiparticle scattering spectroscopy. Philosophical Magazine 92, 3737-3746 (2014)

Pending Articles

• Han Zhao, Omar Mehio, W.K. Park, and L.H. Greene, "Growth of ultra-thin, and uniform planar tunnel junctions on Nb thin films by Atomic Layer Deposition", Thin Solid Films (submitted 2015).
• Wei-Cheng Lee and Laura H. Greene "Point contact spectroscopy as a probe of correlated electron states: Theory and experiment" Reports on Progress in Physics (submitted 2015).
• W.K. Park, L. Sun, A. Noddings, D.-K. Kim, Z. Fisk, and L.H. Greene, “Planar tunneling spectroscopy of the topological surface states in Kondo insulator SmB6” (Submitted).