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

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.