Quantum Spin Hall Effect and Topological Insulators

Stanford University, Stanford CA

Investigators

Abstract

TECHNICAL SUMMARY This award supports theoretical research and education focused on investigating a new topological state of quantum matter. The project will lead to new concepts, the prediction of candidate materials that exhibit topological states, and work with experimentalists to verify their properties. Search for topological states of matter has become an important goal in condensed matter physics. The quantum Hall state gives the first example of a topological state which is characterized by well defined a topological number and described by the topological field theory at low energy. Recently, the theoretical prediction and the experimental observation of the quantum spin Hall state in mercury telluride-cadmium telluride quantum wells provides another example of a new type of topological state. The quantum spin Hall state is a time-reversal invariant bulk insulator, with gapless edge states where opposite spin states counter-propagate. The PI aims to search and design new materials for the topological insulators in two and three dimensions. He plans to systematically investigate the experimentally measurable topological properties of these systems, including the fractional charge, spin-charge separation and the topological magneto-electric effect. He will also investigate topological Mott insulators where the gap arises from strong electronic correlations. The PI is dedicated to the supervision of the PhD. Through the Stanford-IBM center for quantum spintronics, graduate students and postdocs also get broad exposure to the challenges facing the semiconductor industry today. The PI has also been invited to present at the annual press conferences of the Semiconductor Industry Association, sharing both the excitement and the urgency of our research with the general public. NONTECHNICAL SUMMARY This award supports theoretical research integrated with education to elucidate the novel properties of electrons organized in a new state of matter and to predict new materials or specific existing materials where the state can be found. Insulators have been known for a long time; they are a large class of materials that do not conduct electricity. Recently a new kind of insulator, called a topological insulator, was predicted which does not conduct electrons through the bulk but electrons can flow along the edges without dissipation. Materials that are currently being studied in this context include some consisting of alternating layers of mercury telluride and cadmium telluride, the compound bismuth telluride, and alloys composed of bismuth and antimony. Experiments are consistent with theoretical predictions. The PI will carry out theoretical research to further explore these new states of matter and to predict new materials in which they may arise. The study of topological insulators may lead to a new generation of electronic devices that may help to sustain the rapid growth in performance of information technology. The PI is dedicated to the supervision of the PhD. Through the Stanford-IBM center for quantum spintronics, graduate students and postdocs also get broad exposure to the challenges facing the semiconductor industry today. The PI has also been invited to present at the annual press conferences of the Semiconductor Industry Association, sharing both the excitement and the urgency of our research with the general public.