Nonlinear responses induced by inhomogeneous edge states in a centrosymmetric topological insulator

Nonlinear electrical responses, second-order transport effects beyond Ohm’s law, typically arise in systems where inversion symmetry (P) or time-reversal symmetry (T) is broken, such as in non-centrosymmetric crystals exhibiting the nonlinear Hall effect, or in magnetic systems showing non-reciprocal transport. Here, we report the unexpected discovery of nonlinear electrical responses, under T symmetric conditions, in a bulk centrosymmetric, non-magnetic topological insulator, ZrTe5. We show that this nonlinearity is modulated by external magnetic fields, measured position and the Fermi level (EF) shifting, originating from the evolution of inversion symmetry breaking induced by inhomogeneous spatial distributions of surface edge states (ESs). Our findings unveil a mechanism for nonlinear transport in centrosymmetric systems and highlight an additional route for designing nonlinear electronic responses based on topological surface states. Second-order electrical nonlinearity is conventionally thought to originate in crystals with noncentrosymmetric lattices or magnetic order. Here, the authors show another generation paradigm in bulk centrosymmetric, nonmagnetic ZrTe5, arising from an inhomogeneous surface edge-state distribution.