Perspectives of disproportionation driven superconductivity in strongly correlated 3d compounds.
Disproportionation in 3d compounds can give rise to an unconventional electron-hole Bose liquid with a very rich phase diagram, from a Bose metal, to a charge ordering insulator and an inhomogeneous Bose-superfluid. Optimal conditions for disproportionation driven high-T(c) superconductivity are shown to be realized only for several Jahn-Teller d(n) configurations that permit the formation of well defined local composite bosons. These are the high-spin d(4), low-spin d(7), and d(9) configurations given the octahedral crystal field, and the d(1), high-spin d(6) configurations given the tetrahedral crystal field. The disproportionation reaction has a peculiar 'anti-Jahn-Teller' character lifting the bare orbital degeneracy. Superconductivity in the d(4) and d(6) systems at variance with d(1), d(7), and d(9) systems implies unavoidable coexistence of the spin-triplet composite bosons and the magnetic lattice. We argue that unconventional high-T(c) superconductivity, observed in quasi-2d cuprates with tetragonally distorted CuO(6) octahedra and iron-based layered pnictides/chalcogenides with tetrahedrally coordinated Fe(2+) ions presents a key argument to support the fact that the disproportionation scenario is at work in these compounds.
Department of Theoretical Physics, Ural Federal University, 620083 Ekaterinburg, Russia. alexandr.moskvin@usu.ru
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D018011:Chalcogens / Q000737:chemistry*; D003198:Computer Simulation; D003300:Copper / Q000737:chemistry*; D004553:Electric Conductivity; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D007501:Iron / Q000737:chemistry*; D008280:Magnetics; D008956:Models, Chemical
D018011:Chalcogens; D003300:Copper; D007501:Iron; C030973:cupric oxide