Carbonaceous sulfur hydride system: The strong-coupled room-temperature superconductor with a low value of Ginzburg–Landau parameter

Abstract

The superconducting state in a carbonaceous sulfur hydride (C–S–H) system is probably characterized by the record-high critical temperature of 288 K (p≈267 GPa). We determined the properties of the C–S–H superconducting phase within the scope of both classical Eliashberg equations and the Eliashberg equations with vertex corrections. We took into account the scenarios pertinent to either the intermediate or the high value of an electron–phonon coupling constant (λ≈0.75 or λ≈3.3, respectively). The scenario for the intermediate value, however, cannot be actually realized due to the anomalously high value of the logarithmic phonon frequency (ωln/kB=7150 K) it would require. On the other hand, we found it possible to reproduce correctly the value of TC and other thermodynamic quantities in the case of strong coupling, with all the reservations discussed in the presented paper. The vertex corrections lower the order parameter values within the range from ≈50 K to ≈275 K. For the upper critical field HC2≈27 T, the Ginzburg–Landau parameter κ is of the order of 1.7. The strong-coupling scenario for the C–S–H system is also suggested by the high values of λ estimated for H3S (λ≈2.1, κ≈1.5), LaH10 (λ≈2.8–3.9, κ≈1.6), and YH6 (λ≈1.7, κ≈1.3) compounds. In the case of the C–S–H system, we also anticipate the presence of the antiferromagnetic state above the superconducting state like in the dense CS2 superconductor. For p≈174 GPa and TC≈180 K, the magnetic ordering transition occurs at TN≈213 K.