Figure 1: Measurement geometry and helicity dependent photocurrent from the Bi₂Te₃ TI devices.

(a) A schematic picture of the device structure and measurement geometry used in this work. (b) AFM image of the S2 sample showing atomic layer fluctuations, together with the orientation of the surface Brillouin zone. Scale bar, 100 nm. (c,d) Schematic diagrams showing the spin-polarized surface current arising from the CPGE with the optical transitions involving the Dirac cone, illustrating the reverse of the current polarity under the light excitation of a fixed polarization but with varying incident angles θ from (c) a positive to (d) a negative value. (e–g) The helicity-dependent photocurrent as a function of the light incident angle measured at 5 K, obtained from device (e) S1 and (f,g) S2 with the specified excitation wavelengths. Both (the open symbols) and (the filled symbols) are plotted and fitted by equation (2) (the dashed lines), with the fitting parameters given in Table 1. The error bars were estimate from the statistics of 300 data points collected in steady-state measurements.