The Role of Shift Vector in High-Harmonic Generation from Non-Centrosymmetric Topological Insulators under Strong Laser Fields

TL;DR

This paper reveals that the shift vector significantly influences high-harmonic generation in non-centrosymmetric topological insulators, enabling optical detection of topological phase transitions through harmonic emission characteristics.

Contribution

It demonstrates for the first time that the shift vector affects HHG in topological insulators and can be used to identify band inversion during topological phase transitions.

Findings

Shift vector reverses during topological phase transition.

Reversal of shift vector causes opposite harmonic emission timing.

HHG can directly detect band inversion in TIs.

Abstract

As a promising avenue to obtain new extreme ultraviolet light source and detect electronic properties, high-harmonic generation (HHG) has been actively developed in both theory and experiment. In solids lacking inversion symmetry, when electrons undergo a nonadiabatic transition, a directional charge shift occurs and is characterized by shift vector, which measures the real-space shift of the photoexcited electron and hole. For the first time, we have revealed that shift vector plays prominent roles in the real-space tunneling mechanism of three-step model for electrons under strong laser fields. Since shift vector is determined by the topological properties of related wave functions, we expect HHG with its contribution can provide direct knowledge on the band topology in noncentrosymmetric topological insulators (TIs). In both Kane-Mele model and realistic material BiTeI, we have found that the shift vector reverses when band inversion happens during the topological phase transition between normal and topological insulators. Under oscillating strong laser fields, the reversal of shift vector leads to completely opposite radiation time of high-order harmonics. This makes HHG a feasible all-optical strong-field method to directly identify the band inversion in non-centrosymmetric TIs.