Delocalization of topological surface states by diagonal disorder in nodal loop semimetals

Abstract

The effect of Anderson diagonal disorder on the topological surface (drumhead) states of a Weyl nodal loop semimetal (SM) is addressed. Since diagonal disorder breaks chiral symmetry, a winding number cannot be defined. Seen as a perturbation, the weak random potential mixes the clean exponentially localized drumhead states of the SM, thereby producing two effects: (i) the algebraic decay of the surface states into the bulk and (ii) a broadening of the low energy density of surface states of the open system due to degeneracy lifting. This behavior persists with increasing disorder, up to the bulk SM-to-metal transition at the critical disorder Wc. Above Wc, the surface states hybridize with bulk states and become extended into the bulk.