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Universal superconductivity in compositionally complex transition metal alloys

Using a He3 cryostat in a superconducting magnet with fields up to 16 T, superconductivity of (TiZrNbCu)1-xNix and (TiZrNbNi)1-xCux metallic glasses was studied over a broad concentration range from the high entropy alloys (HEA) region to the Ni- and Cu-rich alloys, respectively. We have observed that the upper critical fields of these alloys are Pauli limited and that the superconducting transition temperatures follow the behaviour of the dressed density of states at the Fermi level Nγ(EF), which is common in transition metals and their alloys [1]. In particular, we have shown that the electron-phonon coupling constant λe-p is proportional to the band density of the state at the Fermi level in our alloys, but also crystalline HEAs [2-4], and in other transition metal alloys. This addresses the problem of unusual superconductivity behaviour [4] which was attributed to the chemical complexity of HEAs but is shown to be inherent to transition metals. Although, minor complications do arise from combining metals of different transition series. [1] R. C. Dynes, C. M. Varma, J. Phys. F Met. Phys. 6 (7) (1976) L215-L219 [2] P. Koželj et al, Phys. Rev. Lett. 113 (10) (2014) 107001 [3] S. Vrtnik et al, J. Alloy. Compd. 695 (2017) 3530– 3540 [4] F. von Rohr et al, Proc. Natl. Acad. Sci. 113 (46) (2016) E7144–E7150

High entropy alloys ; Metallic glasses ; Electronic properties ; Hall effect

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