Symmetry indicators in commensurate magnetic flux

We derive a framework to apply topological quantum chemistry in systems subject magnetic flux. start by deriving the action of spatial symmetry operators uniform field, which extends Zak's translation groups all crystal groups. Ultimately, symmetries form projective representation group. As consequence, band representations acquire an extra gauge invariant phase compared non-magnetic theory. Thus, theory indicators is distinct from case. give examples new that appear at $\pi$ Finally, we our results obstructed atomic insulator with corner states field. The reveal topological-to-trivial transition finite flux, confirmed Hofstadter butterfly calculation. bulk provides probe higher order topology certain insulators.