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

Abstract

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.