Glassy atomic vibrations and blurry electronic structures created by local structural disorders in high-entropy metal telluride superconductors

Abstract

Recently, robustness of superconductivity to external pressure has been observed in high-entropy (HE) metal telluride (MTe). Here, we investigated the atomic displacement parameters (Uiso), atomic vibration characteristics, and electronic structure of MTe with various configurational entropies of mixing (ΔSmix) at the M site to understand the origin of the robustness of the superconductivity. Uiso clearly increased by M-site alloying with ΔSmix ≥ 1.1R, which is evidence of the created local disorder in the NaCl-type (low-pressure) phases. The simulated vibrational density of states (DOS) shows remarkable broadening with ΔSmix ≥ 1.1R, which indicates the glassy characteristics of atomic vibrations in the NaCl-type phases. In the calculated electronic structure for the CsCl-type (high-pressure) phases, a blurry electronic band structure appears with increasing ΔSmix, which indicates the evolution of blurry electronic states in HE MTe with the CsCl-type structure. The estimated electronic DOS at the Fermi energy cannot explain the changes in Tc for HE MTe when assuming conventional electron-phonon superconductivity, but the conventional explanation seems to work for PbTe. Therefore, the pairing mechanisms in HE MTe are affected by the glassy phonon and/or blurry electronic states, and the robustness of superconductivity possibly originates from the unique electron-phonon coupling.