Universal Fermi velocity in highly compressed hydride superconductors

TL;DR

This study demonstrates that highly compressed near-room-temperature superconductors share a universal Fermi velocity with high-Tc cuprates, derived from critical field data, despite experimental challenges in direct measurement.

Contribution

The paper introduces a novel method to estimate Fermi velocity in NRTS materials using critical field data, revealing universality across different superconductors.

Findings

NRTS materials exhibit a universal Fermi velocity of approximately 2.1 x 10^5 m/s.

Fermi velocity in NRTS is comparable to high-Tc cuprates.

Derived Fermi velocity depends on the energy gap and critical temperature ratio.

Abstract

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${\Delta}$(0)/(kBTc))*10^5 m/s (where ${\Delta}(0)$ is ground state amplitude of the energy gap). Due to the ratio of 2${\Delta}$(0)/$({k_B}{T_c})$ is varying within a narrow arrange of 3.2 < 2${\Delta}$(0)/$({k_B}{T_c})$ < 5, then $v_F$ in NRTS materials is within the same ballpark with its high-Tc cuprates counterpart.