Characterization of near-room-temperature superconductivity in yttrium superhydrides

TL;DR

This study analyzes the superconducting properties of yttrium superhydrides near room temperature, revealing their unconventional nature and fluctuation-limited transition, based on critical field data and Fermi temperature ratios.

Contribution

It provides the first analysis of the ratio of Tc to Tf in yttrium superhydrides, showing their placement in the unconventional superconductor band and fluctuation-limited transition behavior.

Findings

YH4+YH6 mixture has 0.01 < Tc/Tf < 0.04

Superconducting transition is limited by thermodynamic fluctuations

YH4+YH6 falls in the unconventional superconductor band

Abstract

Recently, Troyan et al (2019 arXiv:1908.01534) and Kong et al (2019 arXiv:1909.10482) extended near-room-temperature superconductors family by new yttrium superhydride polymorphs, YHn (n = 4,6,7,9), which exhibit superconducting transition temperatures in the range of Tc = 210-243 K at pressure of P = 160-255 GPa. In this paper, temperature dependent upper critical field data, Bc2(T), for highly-compressed mixture of YH4+YH6 phases (reported by Kong et al 2019 arXiv:1909.10482) is analysed to deduce the ratio of Tc to the Fermi temperature, Tf. Our analysis shows that in all considered scenarios the YH4+YH6 mixture has the ratio 0.01 < Tc/Tf < 0.04. As the result, YH4+YH6 falls in the unconventional superconductors band in the Uemura plot. It is also found that the characteristic temperature of the order parameter amplitude fluctuations, Tfluc, in the YH4+YH6 mixture is only several percent above observed Tc, and thus the superconducting transition in yttrium superhydride polymorphs is fundamentally limited by thermodynamics fluctuations.