Giant linearly-polarized photogalvanic effect and second harmonic generation in two-dimensional axion insulators

Understand

The second-order nonlinear optical (NLO) processes, such as the photogalvanic effect and second-order harmonic generation (SHG), play crucial roles in probing and controlling light-matter interactions for energy and device applications.

• To date, most studies of second-order NLO processes focus on materials with broken spatial inversion symmetry, such as proper ferroelectrics and noncentrosymmetric Weyl semimetals.
• Nevertheless, inversion symmetry of Shubnikov groups can be broken via spin-ordering in centrosymmetric crystals.
• Unfortunately, these materials are less common, and their NLO responses are usually weak.