A topological phase transition in the Lanthanum Monopnictides as observed with ARPES

The family of binary Lanthanum monopnictides, LaBi, LaSb, and LaAs have attracted a great deal of attention as they display an unusual “extreme” magnetoresistance (XMR) that is not well understood. Possible mechanisms involving non-trivial topology of band structure have been proposed. In this talk, I will present ARPES measurements from LaBi, LaSb, and LaAs which show a clear topological phase transition within the chemical family. The persistence of XMR on either side of this phase transition is incompatible with proposed mechanisms for XMR which involve Z₂ topological order as a prerequisite.