2024/04/05 by Hyeok-Jun Yang, Yang, Hyeok-Jun, Hsu, Yi-Ting · 1 citation
Materials Science · Physics and Astronomy · #Advanced Chemical Physics Studies #FOS: Physical sciences #Organic and Molecular Conductors Research #Physics of Superconductivity and Magnetism #Strongly Correlated Electrons (cond-mat.str-el) #Superconductivity (cond-mat.supr-con)
paper · pdf · doi:10.48550/arxiv.2404.04329
openalex publication_date 2024/04/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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 theoretically show that the number of VHS in the normal state can be qualitatively inferred from the optical absorption spectra Re σii(ω) in the superconducting state. The key feature is the absorption peak at frequency ω=2Δ from the optical transition across the superconducting gap Δ, which is forbidden in a single-band clean superconductor when the inversion symmetry is preserved and the band is quadratic. Although VHS dispersions are mostly quadratic, we find that a divergent peak occurs when there are multiple VHS on the Fermi surface under an applied current. In contrast, we find non-diverging weak peaks when there is only a single VHS. Depending on whether this single VHS has logarithmically or power-law divergent DOS, the peaks in Re σxx(ω) and Re σyy(ω) are nearly isotropic and anisotropic, respectively. Therefore, we propose that experimentally measured peak magnitude and anisotropy in the optical absorption spectra of VH-driven superconductors can be used to determine the number and type of VHS on the Fermi surface. Disorders could even facilitate in distinguishing the multiple and single VHS scenarios since only the diverging peak in the latter case is expected to survive.