Current-induced gap opening in interacting topological insulator surface states

Mark Spencer Rudner, University of Copenhagen

Nonequilibrium many-body systems may host a variety of internal fields, such as dc currents or ac electric fields, which are not allowed in equilibrium. Through electron-electron interactions, such fields may give rise to intriguing feedback effects that lead to novel types of nonlinear transport phenomena and dynamical phase transitions. In this talk I will show how such feedback is manifested in electronic topological edge states. Two-dimensional topological insulators (TIs) host gapless helical edge states that are predicted to support a quantized two-terminal conductance. Quantization is protected by time-reversal symmetry, which forbids elastic backscattering. Paradoxically, the current-carrying state itself breaks the time-reversal symmetry that protects it. As I will discuss, the combination of electron-electron interactions and momentum-dependent spin polarization in helical edge states gives rise to feedback through which an applied current opens a gap in the edge state dispersion, thereby breaking the protection against elastic backscattering. I will discuss transport signatures of this phenomenon and prospects for its realization in recently discovered large bulk band gap TIs, as well as an analogous current-induced gap opening mechanism for the surface states of three-dimensional TIs.

PDF file of the talk available here