Fig. 1. Crystal structure of Bi₂Se₃^[15]_. (a) Stack alternating Bi and Se layers along the z direction and direction selection of surface states; (b) two-dimensional BZ

Fig. 2. Schematic setup of generating photocurrent by linear polarized light

Fig. 3. Relationship between CEP and field intensity and photocurrent generated by surface states parallel or perpendicular to the polarization direction of the optical field at different wavelengths. (a)(b) Relationship between the photocurrent generated by surface states parallel or perpendicular to the direction of the optical field polarization, and the CEP and field strength at a wavelength of 2400 nm; (c)(d) relationship between the photocurrent generated by surface states parallel or perpendicular to the direction of optical field polarization, and CEP and field strength at a wavelength of 3200 nm

Fig. 4. Current between the bands and current within the band under a optical field with a wavelength of 3200 nm. (a) Current between the bands parallel to the polarization direction of the optical field; (b) current within the band parallel to the polarization direction of the optical field; (c) current between the bands perpendicular to the polarization direction of the optical field; (d) current within the band perpendicular to the polarization direction of the optical field

Fig. 5. Under 2400 nm wavelength optical field, photocurrent generated by the body state. (a) Photocurrent parallel to the polarization direction of the optical field; (b) photocurrent perpendicular to the polarization direction of the optical field

Fig. 6. Residual population of conduction bands. (a) Under the optical field with a wavelength of 2400 nm, when CEP=π/2, the curve of the photocurrent variation with the field strength;(b) correspond to the residual population distribution before the reversal of direction at left * point; (c) correspond to the residual population distribution after the reversal of direction at right * point