MOTT INSULATOR TO SUPERCONDUCTOR VIA PRESSURE RVB THEORY PREDICTION OF NEW SYSTEMS

摘要

This paper summarizes my new work, on the nature of Mott transition in orbitally non degenerate spin-1/2 system, motivated by observation of Mott insulator superconductor transition in real systems. The structure of superexchange perturbation theory for a repulsive Hubbard model at half filling is analyzed and it suggests, under some conditions, a resonating valence bond (RVB) mechanism of Mott insulator to superconductor transition; charge 'deconfinement' is accompanied by electron pair delo-calization aided by a preexisting spin singlet correlations in the insulator. An RVB mean field theory at half filling illustrating our mechanism of Mott insulator-Superconductor transition is sketched. We identify some family of compounds as potential candidates for Mott insulator to superconductor transition under pressure: CuO, BaBiO_3, thin films of La_2CuO_4 or CaCuO_2 (infinite layer compound) under pressure or an effective ab-plane pressure/epitaxial compressive stress; synthesizing new compounds such as La_2CuS_2O_2, La_2CuS_4 or CaCuS_2 or compounds containing CuS_2 or CuSe_2 planes to mimic large ab-plane chemical pressure.