Strong electron-phonon coupling superconductivity in compressed ?-MoB2 induced by double Van Hove singularities

Abstract

A recent experiment of MgB2-type structure alpha-MoB2 has realized-32 K superconductivity (SC) at 90 GPa, exhibiting the highest superconducting transition temperature (Tc) among transition-metal diborides. Although the SC was characterized by the electron-phonon coupling (EPC), the microscopic mechanism of how the large EPC constant and high Tc are attained is unclear. Here, based on first-principles calculations, we found that in contrast to MgB2, B atoms contribute most to electronic states near Fermi level (EF), Mo dz2 orbital is more dominant component in MoB2 and provides two impressive peaks in density of states near EF associated with emergent double Van Hove singularities (VHS). The EPC analysis reveals that the electronic sates around double VHS could strongly interact with the softened acoustic modes of Mo out-of-plane vibration, giving rise to a large single gap with the Tc up to-37 K, which distinctly differs from the superconducting feature of MgB2. Furthermore, by electron doping into MoB2, the VHS is tuned to be aligned with the EF and Tc can be increased to-43 K. Our findings not only elucidate the microscopic mechanism of observed high Tc in MoB2, but also demonstrate that MoB2 provides an ideal platform to explore the role of the VHS in emergent strong EPC SC.