Universal Fermi velocity in highly compressed hydride superconductors

Abstract

The Fermi velocity vF is one of the primary characteristics of any conductor, including any superconductor. For conductors at ambient pressure, several experimental techniques have been developed to measure vF, and, for instance, Zhou et al. [Nature 423, 398 (2003)] reported that high-Tc cuprates exhibited a universal nodal Fermi velocity vF,univ=2.7±0.5×105 m/s. However, there have been no measurements of vF in highly compressed near-room-temperature superconductors (NRTS), owing to experimental challenges. Here, to answer the question of the existence of a universal Fermi velocity in NRTS materials, we analyze the full inventory of data on the ground-state upper critical field Bc2(0) for these materials and find that this class of superconductors exhibits a universal Fermi velocity vF,univ=1/1.3×2Δ0/kBTc×105 m/s, where Δ(0) is the ground-state amplitude of the energy gap. The ratio 2Δ0/kBTc varies within a narrow range 3.2≤2Δ0/kBTc≤5, and so vF,univ in NRTS materials lies in the range 2.5 × 105 m/s ≤ vF,univ ≤ 3.8 × 105 m/s, which is similar to the range of values found for the high-Tc cuprate counterparts of these materials. © 2022 Author(s).