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

Abstract

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 λ 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.

The superconducting transition temperatures of C–S–H based on inter-sublattice S−H4-tetrahedron electronic interactions

“…Independently, evidence for unconventional superconductivity in C-S-H is also proposed through analysis of temperature dependence in normal-state resistance, 24 similar to conclusions drawn for H 3 S and LaH 10 . 25 In identifying the pairing mechanism, a mass isotope effect may be considered within the context of observations from H-D isotopic substitutions in related (H/D) 3 S materials.…”

Structure and composition of C-S-H compounds up to 143 GPa

“…[14,15]). Moreover, the whole notion of high-temperature superconductivity is questioned because of the alleged inconsistencies in the superconducting probes [16][17][18].…”

“…However, in the B1 batch sample at 27 GPa additional reflections were observed nearby the reflections belonging to the I4/mcm phase. The new phase was indexed in monoclinic C-centered unit cell with parameters a = 8.255 (16), b = 6.3944 (18), c = 12.14(3) Å, β = 99.3(3) • (Table S5 [28]). This corresponds to the tripling of the I4/mcm unit cell tentatively accounting for very complex Raman spectra observed in this pressure range (see below).…”

Clear evidence against superconductivity in hydrides under high pressure

“…Instead, we have recently argued that the experimental evidence presented so far does not provide conclusive proof of superconductivity in any of these materials [10][11][12][13][14][15][16][17][18][19]. Others have also questioned experimental [20][21][22] and theoretical [23,24] evidence for superconductivity in some of these materials. Therefore, the very existence of high temperature superconductivity in hydrides under pressure is now in question.…”