Spatial distribution of photo-induced anomalous Hall effects of the top and bottom surface states in topological insulators Sb2Te3

Abstract

Three-dimensional (3D) topological insulators (TIs) have attracted much attention due to their topologically protected surface states. Here, we use circularly polarized light to induce the photo-induced anomalous Hall effect (PAHE) in 3D TIs Sb2Te3 thin films with different thicknesses of 5, 7, 12 and 20 quintuple layers (QLs) at room temperature. The dependence of PAHE current on the light spot locations of Sb2Te3 thin films is investigated, which is found to show a completely different behavior from that observed in two-dimensional electron gas (2DEG) systems. This is due to the fact that the total PAHE current is the superposition of the PAHE of the top and bottom surface states. A theoretical model has been proposed to separate the PAHE current of the top and bottom surface states. In addition, as the thickness of the Sb2Te3 film increases from 5 QL to 20 QL, the PAHE currents of the top and bottom surface states first increase and then decrease. The photo-induced anomalous Hall, conductivity of the top surface states in the 7-QL Sb2Te3 film excited by 1064 nm light is as large as 592 nA⋅ V−1⋅ cm ⋅ W−1, which is much larger than that observed in InGaAs/AlGaAs quantum wells (4.45 nA⋅ V−1⋅ cm ⋅ W−1) and GaN/AlGaN heterostructures (1.43 nA⋅ V−1⋅ cm ⋅ W−1). The giant PAHE value observed in Sb2Te3 films suggests that 3D TIs may provide a good platform for spintronic devices.