Control of circular photogalvanic effect of surface states in the topological insulator Bi 2 Te 3 via spin injection.

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