Figure 3

(a–d) Time-domain S-polarized THz waveforms radiated from the (111) surface of n-type Cu_0.02Bi₂Se₃ and p-type Bi₂Te₃ by P- and S-polarized optical pulse excitation. In all polarization configurations, the polarities of S-polarized THz waveforms are reversed when the samples are rotated 180° along the surface normal. A_THz is the peak-to-peak value of the THz waveform. (e–h): the plots of A_THz for the S-polarized THz waveforms as a function of azimuthal angles (-scan) of Cu_0.02Bi₂Se₃ (a,b) and Bi₂Te₃ (c,d) single crystals (black). Obviously, the THz -scans for both single crystals match the XRD -scans for the (1 1 15) peak (green).