Crystalline symmetry-protected non-trivial topology in prototype compound BaAl4

Abstract The BaAl 4 prototype crystal structure is the most populous of all types, and building block for a diverse set sub-structures including famous ThCr 2 Si family that hosts high-temperature superconductivity numerous magnetic strongly correlated electron systems. MA materials (M = Sr, Ba, Eu; A Al, Ga, In) themselves present an intriguing ground states charge spin orders, but have largely been considered as uninteresting metals. We predict exemplary compound to harbor three-dimensional Dirac spectrum with non-trivial topology possible nodal lines crossing Brillouin zone, wherein one pair semi-Dirac points linear dispersion along k z direction quadratic x / y resides on rotational axis C v point group symmetry. An extremely large, unsaturating positive magnetoresistance in despite uncompensated band revealed, quantum oscillations angle-resolved photoemission spectroscopy measurements confirm predicted multiband semimetal pockets holes Van Hove singularity (VHS) remarkably consistent theoretical prediction. thus topological semimetal, casting its status into role vast array materials.