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Bi-Weekly Seminar

Theory of Inhomogeneous High-Temperature Superconductivty

Prof. W. P. Su

by: Prof. W. P. Su

Date: Thursday January 27, 2005

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Inhomogeneity is a hallmark of the high-temperature superconductors as evidenced by many experiments. A natural interpretation of that can be found in a phenomenological model of d-wave superconductivity, which is an extended Hubbard model with onsite repulsion and nearest-neighbor attractive interaction. This model gives rise to a phase diagram which is strikingly similar to the observed one in the cuprates. A central result of the model is that below a critical doping concentration, the system is unstable with respect to phase separation between the antiferromagetic state and the d-wave superconducting state. Such a state has a vanishing compressibility, therefore it is easily rendered inhomogeneous by the random dopant potentials.

As a microscopic origin of the intersite attractive force, a tight-binding version of the Little’s exciton model has been examined. Quantum Monte Carlo calculations indicate that the purely repulsive interaction between conduction electrons and exciton electrons (electronic polarization) can indeed induce phase separation and superconductivity, where are manifestations of the intersite attractive force.

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