Control of Circular Photogalvanic Effect of Surface States in the Topological Insulator Bi₂Te₃ via Spin Injection

The circular photogalvanic effect (CPGE) provides a method utilizing circularly polarized light to control spin photocurrent and will also lead to novel opto-spintronic devices. The CPGE of three-dimensional topological insulator Bi2Te3 with different substrates and thicknesses has been systematically investigated. It is found that the CPGE current can be dramatically tuned by adopting different substrates. The CPGE current of the Bi2Te3 films on Si substrates are more than two orders larger than that on SrTiO3 substrates when illuminated by 1064 nm light, which can be attributed to the modulation effect due to the spin injection from Si substrate to Bi2Te3 films, larger light absorption coefficient, and stronger inequivalence between the top and bottom surface states for Bi2Te3 films grown on Si substrates. The excitation power dependence of the CPGE current of Bi2Te3 films on Si substrates shows a saturation at high power especially for thicker samples, whereas that on SrTiO3 substrates almost linearly increases with excitation power. Temperature dependence of the CPGE current of Bi2Te3 films on Si substrates first increases and then decreases with decreasing temperature, whereas that on SrTiO3 substrates changes monotonously with temperature. These interesting phenomena of the CPGE current of Bi2Te3 films on Si substrates are related to the spin injection from Si substrates to Bi2Te3 films. Our work not only intrigues new physics but also provides a method to effectively manipulate the helicity-dependent photocurrent via spin injection.