Phase transition in quasi-flat-band superconductors

A. A. Zyuzin; A. Yu. Zyuzin

doi:10.1103/tgmg-dvnv

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Phase transition in quasi-flat-band superconductors

A. A. Zyuzin, A. Yu. Zyuzin

DOI 10.1103/tgmg-dvnv · Physical Review B

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Abstract

We investigate superconductivity in a two-dimensional material described by a two-band heavy-fermion model, where hybridization between a dispersive band and a flat band introduces a quasiflat dispersion to the otherwise localized flat-band electrons. The enhanced density of states in the quasiflat band raises the crossover temperature for an inhomogeneous preformed Cooper pair state. The superconducting phase stiffness and the Berezinskii-Kosterlitz-Thouless (BKT) temperature are governed by the Fermi surface contribution induced by hybridization. We compute the crossover and BKT temperatures, revealing a dome-like dependence on doping. When the pairing amplitude exceeds the energy width of the quasiflat band, superconductivity is suppressed, and the inhomogeneous pairing regime expands linearly with increasing interaction strength. However, in the opposite case, the BKT temperature reaches a maximum value that is only numerically less than the energy width of the quasiflat band. We also discuss our results in the context of superconductivity in graphene-based systems.