Unconventional superconductivity in the topological semimetal MoP: Evidence from first-principles calculated electron-phonon coupling

Different from Dirac and Weyl fermion, three-component fermions have no analogue in high-energy physics. Recently, this new fermion was experimentally observed in topological semimetal MoP (Nature 546 (2017), 627). Later, MoP is found to be superconducting below 2.5 K at 30 GPa, and the transition temperature increases with the increasing of pressure. The microscopic paring mechanism in MoP is crucial to topological superconductor but so far unexplored. In this work, we investigate the variation of electron-phonon coupling (EPC) and superconducting critical temperature T-c of MoP with pressures by first-principles calculations. On the one hand, the calculated transition temperature T-c is two orders of magnitude smaller than the experimental value. On the other hand, the calculated EPC strength and Tc decrease monotonically with the increasing of pressure, which is in contradiction with the relation established in experiment. Our results demonstrate that the superconductivity in pressurized MoP cannot be explained within the framework of the conventional electron-phonon pairing mechanism.