The electron-phonon coupling constant, the 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$ by 5 K exceeds previous record of Tc = 280 K reported by Somayazulu et al (2019 Phys. Rev. Lett. 122 027001) for highly-compressed $La$$H_{10}$. In this paper we analyze experimental temperature dependent magnetoresistance data, R(T,B), reported by Snider et al. The analysis shows that $H_x$$(S,C)_y$ compound exhibited Tc = 190 K (P = 210 GPa) has the electron-phonon coupling constant $λ$$_{e-ph}$ = 2.0 and the ratio of critical temperature, Tc, to the Fermi temperature, Tf, in the range of 0.011 < Tc/Tf < 0.018. These deduced values are very close to ones reported for $H_x$$S$ at P = 155-165 GPa by Drozdov et al (2015 Nature 525 73). This means that in all considered scenarios the carbonaceous sulfur hydride 190 K superconductor falls into unconventional superconductors band in the Uemura plot, where all other highly-compressed super-hydride/deuterides are located. It should be noted that that our analysis shows that all raw R(T,B) datasets for $H_x$$(S,C)_y$ samples for which Snider et al (2020 Nature 586 373) reported Tc > 200 K cannot be characterized as reliable data sources. Thus, independent experimental confirmation/disprove high-Tc values in the carbonaceous sulfur hydride is required.

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