Synthesis, crystal and electronic structure, and physical properties of the Mo6Ga31 endohedral cluster superconductor are reported. The compound has two crystallographic modifications, monoclinic and triclinic, in which the same {Mo12Ga62} building units are perpendicular or codirectional to each other, respectively. Monoclinic and triclinic structures of Mo6Ga31 possess qualitatively the same electronic density of states showing a high peak at the Fermi level. Both modifications are inherently present in the bulk specimen. Due to the proximity effect, bulk Mo6Ga31 exhibits single superconducting transition at the critical temperature of 8.2 K in zero magnetic field. The upper critical field, which is 7.8 T at zero temperature, shows clear enhancement with respect to the Werthamer-Helfand-Honenberg prediction. Accordingly, heat capacity measurements indicate strong electron-phonon coupling in the superconducting state with the large ratio of 2Δ(0)/(kBTc)=4.5, where 2Δ(0) is the full superconducting gap at zero temperature.
@article{arxiv.2004.05425,
title = {Mo$_6$Ga$_{31}$ endohedral cluster superconductor},
author = {Valeriy Yu. Verchenko and Alexander O. Zubtsovskii and Alexander A. Tsirlin and Zheng Wei and Maria Roslova and Evgeny V. Dikarev and Andrei V. Shevelkov},
journal= {arXiv preprint arXiv:2004.05425},
year = {2020}
}