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 the topological insulator Bi2Se3.By adopting two-color mid-infrared laser fields on Bi2Se3,we found that the nonlinear response sensitively depends on the relative phase of the driving fields.The even harmonics arise from the sur-face states with a clear signature,whose modulation period equals the cycle of the second-harmonic generation[SHG]field.We reveal that the weak SHG perturbs the nontrivial dipole phase of the electron-hole pair in surface states,and thus leads to the modulation of HHG.It provides a means to manipulate the ultrafast dynamics in surface states through adopting a weak perturbing laser field.