Excitonic effects in shift currents of low dimensional materials from time-dependent GW approach*

We present first-principles studies on shift currents with excitonic effects in 2D materials using an adiabatic time-dependent GW approach. Shift current in a noncentrosymmetric semiconductor is a DC current generated by optical excitations from a nonlinear response processes. Using a newly developed real-time simulation method, we are able to include excitonic effects in the nonlinear responses from first principles, treating the complicated electron-hole interaction at the GW plus Bethe-Salpeter equation level for the first time. We applied this method to study shift currents in monolayer GeS and found strongly enhanced responses due to excitonic effects. Most interestingly, the dominant contributions to the shift currents here are generated at in-gap frequencies, which peaked at energies below the quasi-particle band gap by the exciton binding energies.