Classifying hydrogen-rich superconductors

The era of near-room-temperature superconductivity started after experimental discovery by Drozdov et al (2015 Nature 525 73) who found that compressed H3S exhibits superconducting transition at T-c = 203 K. To date, the record near-room-temperature superconductivity stands with another hydrogen-rich highly compressed compound, LaH10 (Somayazulu et al 2019 Phys. Rev. Lett. 122 027001), which has critical temperature of T-c > 240 K. In this paper, we analyse available upper critical field, B-c2(T), data for LaH10(Drozdov et al 2019 Nature 569 528) and report that this compound in all considered scenarios has the ratio of T-c to the Fermi temperature, T-F, 0.009 < T-c/T-F < 0.038, which is typical range for unconventional superconductors. In attempt to extend our finding, we examined experimental B-c2(T) data for superconductors in the palladium hydrogen system and surprisingly find that PdHx compounds have the ratio of 0.008 < T-c/T-F < 0.012. Taking in account that H3S has the ratio of 0.012 < T-c/T-F < 0.039 (Talantsev 2019 Modern Phys. Lett. B 33 1950195) we come to conclusion that in the Uemura plot all discovered to date hydrogen-rich superconductors, i.e. PdHx, H3S and LaH10, lie in same band as all unconventional superconductors, particularly heavy fermions, fullerenes, pnictides, and cuprates, and former should be classified as a new class of unconventional superconductors.