Non-BCS thermodynamic properties of H2SH2S superconductor

• Thermodynamic properties of the superconducting state in the H2S compound.
• The record high value of superconducting critical temperature.
• The strong-coupling Eliashberg formalism.
• The experimental data confirmed by theoretical results.
• The non-BCS values of the dimensionless ratios connected with thermodynamic functions.

The present paper determines the thermodynamic properties of the superconducting state in the H2SH2S compound. The values of the pressure from 130 GPa to 180 GPa were taken into consideration. The calculations were performed in the framework of the Eliashberg formalism. In the first step, the experimental course of the dependence of the critical temperature on the pressure was reproduced: TC∈〈31,88〉 K, whereas the Coulomb pseudopotential equal to 0.15 was adopted. Next, the following quantities were calculated: the order parameter at the temperature of zero Kelvin (Δ(0)Δ(0)), the specific heat jump at the critical temperature (ΔC(TC)≡CS(TC)-CN(TC)ΔC(TC)≡CS(TC)-CN(TC)), and the thermodynamic critical field (HC(0)HC(0)). It was found that the values of the dimensionless ratios: RΔ≡2Δ(0)/kBTCRΔ≡2Δ(0)/kBTC, RC≡ΔC(TC)/CN(TC)RC≡ΔCTC/CN(TC), and RH≡TCCN(TC)/HC2(0) deviate from the predictions of the BCS theory: RΔ∈〈3.64,4.16〉, RC∈〈1.59,2.24〉, and RH∈〈0.144,0.163〉. Generalizing the results on the whole family of the HnSHnS-type compounds, it was shown that the maximum value of the critical temperature can be equal to ∼290 K, while RΔ,RC and RHRH adopt the following values: 6.53, 3.99, and 0.093, respectively.