Pair-hopping mechanism of superconductivity activated by the nano-space layered structure

Criterion for occurrence of the high-temperature superconductivity by the pair-hopping mechanism in layered materials is given. Based on the multi-reference density functional theory, vanishing inter-layer single particle hopping processes around the Fermi level and appearance of high-energy unoccupied orbitals mediating the Coulomb-repulsion driven pair scattering among the layers in the ordinal band-structure calculation certify appearance of the super-pair-hopping processes as the off-diagonal process of the quantum density–density fluctuation. The criterion is certified for α-K0.25TiNClα-K0.25TiNCl in the band structure calculation using the generalized gradient approximation.

► Mechanism of layered superconductors with unexpectedly high Tc is given. ► The inter-layer pair-hopping mechanism can provide enhancement of Tc. ► Criteria on the pair-hopping mechanism are given. ► Application for an existing material of KxTiNCl is given.