A Gap Protected zero-Hall Effect State in a Semimetal with Glide Symmetry
Abstract: A new direction in topological quantum matter research is the exploration of the large class of nonsymmorphic metals which include glide symmetry operations in their space group (a glide gx =Mx.T is a mirror reflection Mx combined with a fractional translation T in the mirror plane). The layered material KHgSb is analogous to stacking graphene together with distinct ions in the A and B sublattices. A half-lattice translation between adjacent layers renders it nonsymmorphic. KHgSb has been predicted to feature double quantum spin Hall (QSH) surface states in addition to hourglass fermion states. KHgSb displays an unusual anomaly in the quantum limit (lowest Landau level). The onset of a gap suppresses the bulk carrier population exponentially to produce a zero-Hall state with finite diagonal conductance. I will describe the interpretation of this unusual anomaly in terms of QSH states.