Characterization of the superconducting phase in tellurium hydride at high pressure

TL;DR

This study investigates the superconducting phase of tellurium hydride at 300 GPa, revealing strong-coupling effects and higher critical temperature predictions beyond BCS theory, emphasizing the importance of advanced models for such materials.

Contribution

The paper provides a detailed analysis of tellurium hydride's superconducting properties at high pressure using Migdal-Eliashberg equations, highlighting deviations from BCS predictions and emphasizing strong-coupling effects.

Findings

Critical temperature T_c = 52.73 K exceeds BCS estimates.

Thermodynamic ratios surpass BCS limits, indicating strong coupling.

Effective electron mass differs from the bare electron mass.

Abstract

At present, hydrogen-based compounds constitute one of the most promising classes of materials for applications as a phonon-mediated high-temperature superconductors. Herein, the behavior of the superconducting phase in tellurium hydride (HTe) at high pressure ($p=300$ GPa) is analyzed in details, by using the isotropic Migdal-Eliashberg equations. The chosen pressure conditions are considered here as a case study which corresponds to the highest critical temperature value ($T_{c}$) in the analyzed material, as determined within recent density functional theory simulations. It is found that the Migdal-Eliashberg formalism, which constitutes a strong-coupling generalization of the Bardeen-Cooper-Schrieffer (BCS) theory, predicts that the critical temperature value ($T_{c}=52.73$ K) is higher than previous estimates of the McMillan formula. Further investigations show that the characteristic dimensionless ratios for the the thermodynamic critical field, the specific heat for the superconducting state, and the superconducting band gap exceeds the limits of the BCS theory. In this context, also the effective electron mass is not equal to the bare electron mass as provided by the BCS theory. On the basis of these findings it is predicted that the strong-coupling and retardation effects play pivotal role in the superconducting phase of HTe at 300 GPa, in agreement with similar theoretical estimates for the sibling hydrogen and hydrogen-based compounds. Hence, it is suggested that the superconducting state in HTe cannot be properly described within the mean-field picture of the BCS theory.