Quantifying the Nonadiabaticity Strength Constant in Recently Discovered Highly Compressed Superconductors

Abstract

Superconductivity in highly pressurized hydrides has become the primary direction for the exploration of the fundamental upper limit of the superconducting transition temperature, Tc, after Drozdov et al. (Nature 2015, 525, 73) discovered a superconducting state with Tc=203 K in highly compressed sulfur hydride. To date, several dozen high-temperature superconducting polyhydrides have been discovered and, in addition, it was recently reported that highly compressed titanium and scandium exhibit record-high Tc (up to 36 K). This exceeded the Tc=9.2 K value of niobium many times over, which was the record-high Tc ambient pressure metallic superconductor. Here, we analyzed the experimental data for the recently discovered high-pressure superconductors (which exhibit high transition temperatures within their classes): elemental titanium (Zhang et al., Nature Communications 2022; Liu et al., Phys. Rev. B 2022), TaH3 (He et al., Chinese Phys. Lett. 2023), LaBeH8 (Song et al., Phys. Rev. Lett. 2023), black phosphorous (Li et al., Proc. Natl. Acad. Sci. 2018; Jin et al., arXiv 2023), and violet (Wu et al., arXiv 2023) phosphorous to reveal the nonadiabaticity strength constant TθTF (where Tθ is the Debye temperature, and TF the Fermi temperature) in these superconductors. The analysis showed that the δ-phase of titanium and black phosphorous exhibits TθTF scores that are nearly identical to those associated with A15 superconductors, while the studied hydrides and violet phosphorous exhibit constants in the same ballpark as those of H3S and LaH10.