Emergent Quantum Phenomena in Topological Kondo Insulators

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Non-Technical AbstractThis award from the Condensed Matter Physics program of the Division of Materials Research supports research on the electronic properties of a new class of material known as Topological Insulators. A topological insulator is an unusual quantum state in which the bulk of the material is an electrical insulator, while the surface is a conductor that is stable against various external perturbations. Topological insulators have generated great scientific excitement over the past few years because of the novel electrical properties and their potential application as advanced electronic devices in areas such as quantum computation and spin transport. However, all of the materials discovered to date have a non-insulating bulk transport behavior because of unavoidable defects in the material; therefore, they do not exhibit ideal or useful topological properties. A recent theory has suggested that a special class of material, known as a Kondo insulator, would be a topological insulator with a true bulk insulating state. Researchers at the University of Maryland conduct measurements of the electronic properties of known Kondo insulators to investigate their possible topological behavior and to test their suitability for new and novel electronic applications. This research project involves the training of undergraduate and graduate students in advanced measurement techniques and in cutting edge scientific knowledge of materials physics.Technical AbstractResearchers at the University of Maryland are undertaking experimental studies of electronic transport phenomena in different Kondo insulator systems that are theoretically suggested to harbor topological surface states. Understanding the novel properties of topological insulators and the role of strong electron correlations on topological properties is a major basic science problem in condensed matter physics. The recent discovery of a surface metallic state in the Kondo insulator SmB6 suggests that strongly correlated TIs may exist. However, despite many unconventional transport phenomena recently found in SmB6, the "smoking gun" evidence for a nontrivial topological surface state has yet to been established. This study emphasizes the transport properties of thin films and single crystals at low temperatures (down to 20 mK), where novel emergent quantum phenomena are expected to be prominent. The project uses point contact spectroscopy, static electric field effect studies, and high magnetic field transport measurements and microwave and optical measurements on promising KI materials. An important thrust of this project is the study of the proximity effect, since it has been predicted that incorporating topological insulators with ferromagnetic insulators and/or conventional superconductors may lead to exotic properties such as Majorana fermion excitations. All the materials required for these measurements are being synthesized and characterized in-house. This research project involves the training of undergraduate and graduate students in advanced measurement techniques and in cutting edge scientific knowledge of materials physics.