Electron counting and chemical complexity in theTa-Nb-Hf-Zr-Ti HEA superconductors

High-entropy alloys (HEAs) are a new class of materials that consist of several principal elements arranged on simple lattices. These structures are stabilized by the high configurational entropy of the random mixing of the elements. The recently discovered Ta-Nb-Hf-Zr-Ti HEA superconductor appears to display properties of both crystalline intermetallics and amorphous materials; e.g., it has a well-defined superconducting transition along with an exceptional robustness against disorder. In this presentation, we will show that the properties of these superconducting HEAs are strongly related to the electron count and that the T_cs of these alloys fall between those of analogous crystalline and amorphous materials [1-3]. We find that despite the large degree of randomness and disorder in HEAs, the superconducting properties are nevertheless strongly dependent on the chemical composition and complexity. We argue that HEAs are excellent model systems for understanding how superconductivity evolves from crystals to amorphous solids.

[1] F.O. von Rohr, M. Winiarski, J. Tao, T. Klimczuk, and R.J. Cava, PNAS 113, E7144 (2016).
[2] J. Guo, et al. PNAS 114, 50 (2017).
[3] F.O. von Rohr, R.J. Cava, PRM 2, 034801 (2018).