Giant photoinduced anomalous Hall effect of the topological surface states in three dimensional topological insulators Bi_2Te_3

摘要

Topological insulators (TIs) are considered as ideal spintronic materials due to the spin-momentum-locked Dirac surface states. The photoinduced anomalous Hall effect (PAHE) is a powerful tool to investigate the spin Hall effect of topological insulators even at room temperature. In this Letter, the PAHE has been observed in three dimensional topological insulator Bi_2Te_3 thin films grown on Si substrates at room temperature. As the thickness of the Bi_2Te_3 films increases from 3 to 20 quintuple layer (QL), the PAHE first increases and then decreases, and it reaches a maximum at 7 QL. The sign reversal of the PAHE of the 3 QL sample after oxidation reveals that the PAHE of the Bi_2Te_3 thin films is dominated by the top surface states, which is further confirmed by the circular photogalvanic effect under front and back illuminations. The photoinduced anomalous Hall conductivity excited by 1064 nm light is as large as 5.28 nA V~(-1) W~(-1) cm~2 in the 7 QL sample, much larger than that observed in InGaAs/AlGaAs quantum wells (0.445 nA V~(-1) W~(-1) cm~2) and GaN/AlGaN heterostructures (0.143 nA V~(-1) W~(-1) cm~2). By comparing the PAHE current excited by 1064 nm with that excited by 1342 nm, we reveal that the tremendous PAHE excited by 1064 nm light is due to the modulation effect of spin injection from Si substrates. The giant PAHE value observed in TI Bi_2Te_3 may offer spintronic applications of TIs such as high-efficient light-polarization-state detectors.