Universal Fermi velocity in highly compressed hydride superconductors

Fermi velocity, $v_F$, is one of the primary characteristics of any conductor, including superconductors. For conductors at ambient pressure several experimental techniques have been developed to measure $v_F$ and, for instance, Zhou et al (Nature 423 398 (2003)) reported that high-Tc cuprates exhibit universal nodal Fermi velocity of $v_F$ = $2.7*10^5$ m/s. However, there were no experimental techniques applied to measure $v_F$ in highly-compressed near-room-temperature superconductors (NRTS), due to experimental challenges. Here to answer a question about the existence of the universal Fermi velocity in NRTS materials, we analyzed full inventory of the ground-state upper critical field data, Bc2(0), for these materials and found that this class of superconductors exhibits universal Fermi velocity of $v_F$ = (1/1.3)*(2$Δ$(0)/(kBTc))*10^5 m/s (where $Δ(0)$ is ground state amplitude of the energy gap). Due to the ratio of 2$Δ$(0)/$({k_B}{T_c})$ is varying within a narrow arrange of 3.2 < 2$Δ$(0)/$({k_B}{T_c})$ < 5, then $v_F$ in NRTS materials is within the same ballpark with its high-Tc cuprates counterpart.

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