T_cSUH Special Seminars

Friday, April 24, 2009

Room 102, University of Houston Science Center

12:00 PM - 01:00 PM

By using a variational appproach it is shown that periodic stripe states or randomly oriented stripe states are almost degenerate in energy with the uniform d-wave superconducting state in the t-J type models. It provides a simple explanation for the observation of the cluster-glass state in BSCO high temperature superconductors. There is no need to introduce other competing interactions to obtain these inhomogeneous states. However, to stabilize a long-range-order stripe state as seen in LaBaCuO with 1/8 doping, we propose a new model to include in the t-J model the short-ranged hopping modulations due to mass renormalization by electron-phonon coupling. In addition, our results show that the most stable stripe will have its charge modulation period scales with 1/2x where x is the hole density. Hence we are able to explain the so called Yamada plot observed in neutron scattering experiment.

T. K. Lee received the B.S. degree from National Taiwan University (Taipei) in 1971, and the Ph.D. in Physics from Brown University in 1975. He was a Research Associate in the Department of Physics at City College of City University, New York from 1975 to 1979, and at the Institute for Theoretical Physics at the University of California at Santa Barbara from 1979 to 1981. He was Assistant Professor and Professor of Physics at Virginia Polytechnic Institute and State University, Blacksburg, VA, from 1982 to 1997. In 1996, he became a Research Fellow at the Institute of Physics, Academia Sinica in Taipei, and in 1997, also became Head of the Physics Division, National Center for Theoretical Sciences, Hsinchu, Taiwan. From 1997 to 2002, he was Outstanding Scholarship Chair. Dr. Lee's research interests include high temperature superconductivity, nano-materials, X-ray crystallography, protein structure, protein folding, and Quantum Monte Carlo method.

Professor Margaret Cheung joined the University of Houston as a junior faculty member in 2006. Research projects include development of physics principles and application of high-performance computing methods for studying various topics in theoretical biophysics, soft condensed matter, and nano-scale materials.Professor Cheung received her B.S. in Chemistry from National Taiwan University and her Ph.D. in Physics from the University of California, San Diego. She was a Sloan Postdoctoral Fellow in Computational Biology at the University of Maryland.