Extremely high conductivity in the unconventional triple point fermion material MoP

Weyl and Dirac fermions have created much attention in condensed matter physics and materials science. Recently, several additional distinct types of fermions have been predicted. Depending on the inherent symmetry of a particular compound, the crossing points can be several-fold degenerate: two- and four-fold degenerate points are classified as Weyl and Dirac types, respectively. New materials going beyond Weyl and Dirac with higher band degeneracies have been proposed. MoP, a triple point Fermion material, shows characteristic like a correlated metal with anomalously high conductivity. Consistently, the momentum relaxing time of the electrons is found to be ~ 100 times larger than the momentum conserving time. We also find a strong violation of the Wiedemann-Franz law below ~ 40 K, the same temperature where a large magnetoresistance develops. These peculiar observations strongly indicate the role of hydrodynamic flow of charge carriers for extremely high conductivity in MoP. Our study opens a new window for hydrodynamic flow of fermions in low resistive topological metals.