Critical Exponents for the Quantum Hall and Quantum Spin Hall Effect
Speaker: Tomi Ohtsuki, Sophia University, Tokyo
Series: Topical Seminars
Location: Engineering Quadrangle B205
Date/Time: Tuesday, October 9, 2012, 4:00 p.m. - 5:00 p.m.
he plateau transitions of the quantum Hall effect is one of the most extensively studied quantum critical phenomena in condensed matter physics. It is described by the exponent \nu, which describes the divergence of the localization length. Experimentally, the exponent is related to the slope of the Hall conductivity between the plateaus.
Since the discovery of the quantum Hall effect, the critical exponent has been studied extensively, but the precise value remains elusive. One of the difficulties is the occurrence of corrections to scaling, which change only very gradually with the system size. These slowly changing corrections make it numerically very demanding to estimate the behavior in the thermodynamic limit. A few years ago, we succeeded in estimating the value to be 2.59, which is significantly larger than the previously widely accepted value of 2.37. We discuss the implication of this new value for experiment and the conformal field theory. We also report the estimate of \nu for quantum spin Hall effect, which seems to be consistent with the values for the standard symplectic universality class.
Tomi Ohtsuki is Professor of Physics at Sophia University in Tokyo, Japan. He obtained his Doctor of Science at the University of Tokyo in 1989. Following postdoctoral fellowships with the Japanese Society for the Promotion of Science, at PTB Braunschweig (Germany) and at Osaka University, Dr. Ohtsuki joined the faculty at Toho University in 1992, and moved to Sophia University in 1995 as Associate Professor of Physics, and was promoted to Professor in 2001. Professor Ohtsuki specializes in theoretical and computational condensed matter physics. His recent research has focused on quantum transport phenomena including the Anderson transition, conductance fluctuations, and Hall and spin Hall effects in nanoscale systems.