Condensed Matter Physics Seminar

Friday, January 29, 1999, 2 p.m.
Plant Sciences Building, Room 1130

Unified theory of superconductivity and antiferromagnetism in the high-Tc cuprates

Eugene Demler

(Institute for Theoretical Physics, University of California at Santa Barbara)

Abstract:  Understanding the microscopic mechanism of high $T_c$ superconductivity requires quantitatively accounting for the superconducting condensation energy.  Within the $t$-$J$ model of copper-oxides, the condensation energy can be related to the change in the dynamical spin structure factor between the superconducting and the normal states.  By analyzing previous experimental data, we show that the change associated with the resonant neutron scattering peak found in $YBa_2Cu_3O_7$ can quantitatively account for the condensation energy. We argue that this analysis suggests a microscopic mechanism for high $T_c$ superconductivity, where antiferromagnetic exchange energy is saved in the superconducting state through the coupling to a triplet particle-particle resonance. A review of this collective mode in the t-J and Hubbard models is given and its role in unifying d-wave superconductivity and antiferromagnetism into SO(5) symmetry will be shown. Effective low energy SO(5) theory of the high Tc cuprates is considered and effect of the fermions is discussed. Possible experimental tests are reviewed.

Host: Sankar Das Sarma

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