Among the diverse family of unconventional superconductors, Chevrel phases (CPs) are distinguished by their remarkably high upper critical fields, often exceeding the Pauli paramagnetic limit [1]. A multiband superconductivity scenario—potentially involving strong coupling effects and enhanced spin–orbit scattering—has long been proposed as a plausible explanation [2]. The recent discovery of superconductivity in K1+δMo6Se8 introduces a new platform to revisit these questions [3]. Notably, this compound exhibits an upper critical field of approximately 27 T, significantly exceeding the expected Pauli limit. By combining low-temperature specific heat measurements with point-contact spectroscopy, we provide compelling evidence for multiband superconductivity in K1+δMo6Se8. The observed behavior closely resembles that of other Chevrel phase superconductors such as SnMo6S8 and PbMo6S8. These results suggest that multiband superconductivity is a generic feature of Chevrel phases and likely plays a key role in their exceptionally high upper critical fields.

References:

[1] Ø. Fischer, Appl. Phys. 16, 1 (1978).

[2] M. Decroux and Ø. Fischer, Topics in Current Physics: Superconductivity in Ternary Compounds II (Springer Verlag, Berlin, 1982), pp. 57–87.

[3] Y. Q. Shi et al., J. Am. Chem. Soc. 147, 22453 (2025).