Distinguishing high-harmonic generation from surface and bulk states in topological insulator Bi2Se3

We demonstrated a scheme to differentiate the high-harmonic generation (HHG) originating from the surface states and bulk states of thetopological insulator (TI) Bi2Se3. By adopting two-color mid-infrared laser fields on Bi2Se3, we found that the nonlinear response sensitivelydepends on the relative phase of the driving fields. The even harmonics arising from the surface states with a clear signature, whose modulationperiod equals the cycle of the second-harmonic generation (SHG) field. We reveal that the weak SHG perturbs the nontrivial dipole phase ofthe electron-hole pair in surface states, and thus leads to the modulation of HHG. It provides a means to manipulate the ultrafast dynamics insurface states through adopting a weak perturbing laser field.