Study of the superconducting state in the Cmmm phase of GeH4 compound

TL;DR

This study characterizes the superconducting state of GeH4 in the Cmmm phase under 20 GPa, revealing high critical temperatures and thermodynamic parameters that deviate from classical BCS predictions across a range of Coulomb pseudopotentials.

Contribution

The paper provides a detailed analysis of the thermodynamic properties of GeH4's superconducting state, highlighting deviations from BCS theory and exploring the effects of Coulomb pseudopotential variations.

Findings

Critical temperature ranges from 54.54 to 31.23 K.

Energy gap to T_C ratio varies from 4.07 to 3.88.

Specific heat jump ratio decreases from 1.85 to 1.69.

Abstract

A superconducting state, that induces in ${\rm GeH_{4}}$ under the pressure at 20 GPa, is being characterized by a high critical temperature $T_{C}\in<54.54,31.23>$ K, for a wide range of the Coulomb pseudopotential $\mu^{\star}\in<0.1,0.3>$. Other thermodynamic parameters for the considered range of the Coulomb pseudopotential significantly differ from the predictions of a classical BCS theory. In particular: (i) the ratio of the energy gap to the critical temperature ($R_{\Delta}\equiv 2\Delta(0)/k_{B}T_{C}$) changes from 4.07 to 3.88; (ii) the value of the parameter $R_{C}\equiv\Delta C(T_{C})/C^{N}(T_{C})$ decreases from 1.85 to 1.69, where $\Delta C$ denotes the specific heat's jump, and $C^{N}$ is the specific heat of the normal state; (iii) the ratio $R_{H}\equiv T_{C}C^{N}(T_{C})/H^{2}_{C}(0)$, where $H_{C}(0)$ represents the low - temperature thermodynamic critical field, increases from 0.147 to 0.155.