The electron-phonon coupling constant, Fermi temperature and unconventional superconductivity in the carbonaceous sulfur hydride 190 K superconductor

Recently, Snider et al (2020 Nature 586 373) reported on the observation of superconductivity in highly compressed carbonaceous sulfur hydride, H-x(S,C)(y). The highest critical temperature in H-x(S,C)(y) exceeds the previous record of T-c = 280 K by 5 K, as reported by Somayazulu et al (2019 Phys. Rev. Lett. 122 027001) for highly compressed LaH10. In this paper, we analyze experimental temperature-dependent magnetoresistance data, R(T,B), reported by Snider et al. The analysis shows that H-x(S,C)(y) compound exhibited T-c = 190 K (P = 210 GPa), has the electron-phonon coupling constant lambda(e-ph) = 2.0 and the ratio of critical temperature, T-c, to the Fermi temperature, T-F, in the range of 0.011 T-c/T-F 0.018. These deduced values are very close to the ones reported for H3S at P = 155-165 GPa (Drozdov et al 2015 Nature 525 73). This means that in all considered scenarios the carbonaceous sulfur hydride 190 K superconductor falls into the unconventional superconductor band in the Uemura plot, where all other highly compressed super-hydride/deuterides are located. It should be noted that our analysis shows that all raw R(T,B) data sets for H-x(S,C)(y) samples, for which Snider et al (2020 Nature 586 373) reported T-c > 200 K, cannot be characterized as reliable data sources. Thus, independent experimental confirmation/disproof for high-T-c values in the carbonaceous sulfur hydride are required.

Automated summary

Recent research has found superconductivity in highly compressed carbonaceous sulfur hydrides with a critical temperature of 190 K. The properties of this material are similar to those of H3S, suggesting that it falls into the category of unconventional superconductors. Further independent experimental confirmation is needed to verify the high critical temperature values reported by Snider et al.