Tuning of circular photogalvanic effect of surface states in the topological insulator Sb2Te3 via structural deformation

Strain is a useful method to manipulate properties of three-dimensional (3D) topological insulators (TIs). In this study, we demonstrate the possibility to tune the circular photogalvanic effect (CPGE) of surface states of 3D TI Sb2Te3 films by applying external strain. The CPGE of 3D TI Sb2Te3 grown on SrTiO3 (STO) with different thicknesses has been systematically investigated. It is found that as the thickness of Sb2Te3 films increases from 7-quintuple layer (QL) to 27-QL, the CPGE current first increases and then decreases. Additionally, the CPGE currents demonstrate remarkable temperature dependence, which even reverse sign when the temperature is increased from 77 to 300 K. This phenomenon is due to the vertical thermoelectric effect and inverse spin Hall effect. Finally, the CPGE measurements of Sb2Te3 films under different mechanical strains are performed, and it is found that the CPGE current linearly decreases with the increase in the external strain. The variation in the CPGE current can be tuned up to 11% and 44% in the 18- and 12-QL Sb2Te3 grown on STO substrates under a tensile strain of 0.0225 and 0.0066, respectively. In particular, it can even reach 100% in the 30-QL Sb2Te3 film grown on an InP substrate under a tensile strain of 0.0033, which is due to the combined effect of mechanical deformation and spin injection from substrates. Our work provides a method to effectively manipulate the CPGE in 3D TIs by the combined effect of mechanical strain and spin injection from substrates, which paves the way for novel opto-spintronic devices.