A first principles study of the X₃M₈ (X = V, Nb, Ta and M = Cl, Br, I) materials family

The two-dimensional kagome material, Nb₃Cl₈, has been the subject of intense current interest because it has been predicted to host a flat half-filled kagome band. Experimentally, there is evidence of Mott insulating behavior at high temperatures and the presence of a structural phase transition coexisting with a poorly understood magnetic transition at low temperatures. Here, by using first-principles modeling, we explore both bulk and monolayers of X₃M₈ (X = V, Nb, Ta and M = Cl, Br, I) to understand the role of spin-orbit coupling in driving the atomic, electronic and magnetic structure of this materials family. We discuss the stability of the high and low temperature ground states and the associated structural and magnetic transitions and delineate how these transitions are affected by hole doping. Finally, the theoretical predictions are compared with the results of corresponding angle-resolved photoemission experiments.