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

The superconducting state, that gets induced in the GeH4 compound under the pressure at 20 GPa, is characterized by the high critical temperature T C ( μ ⋆ ) ∈ 〈 54.5 , 31.2 〉 K, where μ ⋆ is the Coulomb pseudopotential, and μ ⋆ ∈ 〈 0.1 , 0.3 〉 . Other thermodynamic parameters for the considered range of the Coulomb pseudopotential significantly differ from the predictions of the BCS model. In particular: (i) the ratio of the energy gap to the critical temperature ( R Δ ≡ 2 Δ ( 0 ) / k B T C ) changes from 4.07 to 3.88; (ii) the value of the parameter R C ≡ Δ C ( T C ) / C N ( T C ) decreases from 1.85 to 1.69, where Δ C denotes the specific heat jump, and CN is the specific heat of the normal state; (iii) the ratio R H ≡ T C C N ( T C ) / H C 2 ( 0 ) increases from 0.147 to 0.155; HC represents the thermodynamic critical field.