Optical absorption signatures of superconductors driven by Van Hove singularities

Hyeok-Jun Yang; Yi-Ting Hsu

doi:10.1103/PhysRevB.111.054514

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Optical absorption signatures of superconductors driven by Van Hove singularities

Hyeok-Jun Yang, Yi-Ting Hsu

DOI 10.1103/PhysRevB.111.054514 · Physical Review B

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Abstract

Due to the diverging density of states (DOS), Van Hove singularities (VHS) near the Fermi level are known to boost the susceptibility to a wide variety of electronic instabilities, including superconductivity. We propose that the number and type of VHS on the Fermi surface can be detected by the optical conductivity in the superconducting state under an applied current. We theoretically show that having multiple VHS on the Fermi surface is a novel mechanism for activating a divergent optical absorption peak at frequency ω=2Δ, resulting from the transition across the gap Δ which is forbidden in single-band clean superconductors with inversion symmetry and quadratic bands. In contrast, we find a weak peak with nondivergent intensity when there is only a single VHS. Whether its DOS has logarithmic or power-law divergence can be detected by the anisotropy between the peaks in σxx(ω) and σyy(ω). Our prediction can be tested by measurements of optical absorption spectra in monolayer, few-layer, or thin-film superconductors with VHS on the Fermi surface.