Undamped plasmon modes and enhanced superconductivity in metal diborides

Abstract

Abstract The anisotropic geometric and electronic structures of metal diborides (MB2) leads to many unusual optical and electronic properties. Here, we present a first-principles study on the low-energy collective electronic excitations and the superconducting performance of the MB2 (M = Be, Mg, Al, and Ca). We demonstrate the undamped cosine-like plasmon modes and the sine-like acoustic plasmons in these metal diborides. Interestingly, the energy of the acoustic plasmons shows a positive correlation with the E 2g phonon modes which are negatively correlated with the superconducting transition temperature (T c) of the MB2 materials. Moreover, hole doping can lower the energy of the acoustic plasmons and enhance the T c of CaB2 up to 48.2 K. Our work offers a theoretical guidance to regulate the plasmonic properties, as well as a new predictive factor for superconductivity.