Search

Helicity-dependent photocurrent (HDPC) of the topological surface states (TSSs) in the intrinsic magnetic topological insulator MnBi2Te4 is investigated. It is revealed that the HDPC is mainly contributed by the circular photogalvanic effect (CPGE) current when the incident plane is perpendicular to the connection of the two electrodes, while the circular photon drag effect plays the dominant role when the incident plane is parallel to the connection of the two electrodes. The CPGE current shows an odd function dependence on incident angles, which is consistent with the C 3 v symmetry group of the TSSs in MnBi2Te4. The amplitude of the CPGE current increases with the decrease in temperature, which can be attributed to the increase in mobility at low temperatures, confirmed by the transport measurements. Furthermore, we modulate the CPGE of MnBi2Te4 by applying top gate and source–drain voltages. Compared to Bi2Te3 of the same thickness, the CPGE current of MnBi2Te4 can be more effectively tuned by the top gate because the Fermi level of MnBi2Te4 can be effectively regulated by the top gate, and it is tuned across the Dirac point. This work suggests that the intrinsic magnetic topological insulator MnBi2Te4 is a good candidate for designing opto-spintronics devices. [ABSTRACT FROM AUTHOR]

Circular photogalvanic effect (CPGE) of single-crystalline ternary topological insulator Bi 2 (Te 0.23 Se 0.77) 3 nanowires, which are synthesized by the chemical vapor deposition, have been investigated. It is demonstrated that the distributions of the elements in the nanowires are fairly uniform, and they have high crystal quality. Compared with Bi 2 Se 3 nanowires, the ternary Bi 2 (Te 0.23 Se 0.77) 3 nanowires have better responsivity to circularly polarized light. The incident angle dependence of the CPGE current indicates that the symmetry of the surface states of the nanowire belongs to C 3 v symmetry. The temperature dependence of the CPGE current is also investigated. As the temperature decreases from 300 to 77 K, the CPGE current first increases and then decreases, which is due to the variation of the mobility and photo-generated carrier density with temperature. Our work suggests that ternary Bi 2 (Te 1 − x Se x) 3 nanowires are good candidates for designing polarization-sensitive photoelectric devices. [ABSTRACT FROM AUTHOR]

A hallmark signature of the three-dimensional (3D) topological insulator (TI) is that the spin-momentum locked massless Dirac fermions populate its surface states, where the carrier spins are locked to their momentum. Here, we report on the magnetic-field induced helicity dependent photogalvanic effect (MHPGE) of 3D TI thin films Bi 2 Te 3 or (Bi x Sb 1 − x ) 2 Te 3 of different thicknesses excited by near-infrared (1064 nm) under an in-plane magnetic field. It is found that the MHPGE current J c x under the longitudinal geometry, i.e., J c x ∥ B x , is induced by the Larmor procession, while that under the transverse geometry, i.e., J c x ∥ B y , is mainly introduced by the hexagonal warping, which can be enhanced by the in-plane magnetic field. Our work demonstrates the possibility to tune the spin-polarized photocurrent of the surface states in 3D TIs via a magnetic field, which may be utilized to design new kinds of opto-spintronic devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Bi2Te3 thin films grown on Si substrates at room temperature. As the thickness of the Bi2Te3 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 Bi2Te3 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 cm2 in the 7 QL sample, much larger than that observed in InGaAs/AlGaAs quantum wells (0.445 nA V−1 W−1 cm2) and GaN/AlGaN heterostructures (0.143 nA V−1 W−1 cm2). 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 Bi2Te3 may offer spintronic applications of TIs such as high-efficient light-polarization-state detectors. [ABSTRACT FROM AUTHOR]

Helicity-dependent photocurrent (HDPC) of the topological surface states (TSSs) in the intrinsic magnetic topological insulator MnBi2Te4 is investigated. It is revealed that the HDPC is mainly contributed by the circular photogalvanic effect (CPGE) current when the incident plane is perpendicular to the connection of the two electrodes, while the circular photon drag effect plays the dominant role when the incident plane is parallel to the connection of the two electrodes. The CPGE current shows an odd function dependence on incident angles, which is consistent with the C 3 v symmetry group of the TSSs in MnBi2Te4. The amplitude of the CPGE current increases with the decrease in temperature, which can be attributed to the increase in mobility at low temperatures, confirmed by the transport measurements. Furthermore, we modulate the CPGE of MnBi2Te4 by applying top gate and source–drain voltages. Compared to Bi2Te3 of the same thickness, the CPGE current of MnBi2Te4 can be more effectively tuned by the top gate because the Fermi level of MnBi2Te4 can be effectively regulated by the top gate, and it is tuned across the Dirac point. This work suggests that the intrinsic magnetic topological insulator MnBi2Te4 is a good candidate for designing opto-spintronics devices. [ABSTRACT FROM AUTHOR]

A hallmark signature of the three-dimensional (3D) topological insulator (TI) is that the spin-momentum locked massless Dirac fermions populate its surface states, where the carrier spins are locked to their momentum. Here, we report on the magnetic-field induced helicity dependent photogalvanic effect (MHPGE) of 3D TI thin films Bi 2 Te 3 or (Bi x Sb 1 − x ) 2 Te 3 of different thicknesses excited by near-infrared (1064 nm) under an in-plane magnetic field. It is found that the MHPGE current J c x under the longitudinal geometry, i.e., J c x ∥ B x , is induced by the Larmor procession, while that under the transverse geometry, i.e., J c x ∥ B y , is mainly introduced by the hexagonal warping, which can be enhanced by the in-plane magnetic field. Our work demonstrates the possibility to tune the spin-polarized photocurrent of the surface states in 3D TIs via a magnetic field, which may be utilized to design new kinds of opto-spintronic devices. [ABSTRACT FROM AUTHOR]

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 Sb 2 Te 3 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 Sb 2 Te 3 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 Sb 2 Te 3 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 Sb 2 Te 3 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 Sb 2 Te 3 films suggests that 3D TIs may provide a good platform for spintronic devices. • The spatial distribution of the PAHE currents has been investigated in the Sb 2 Te 3 film. • A model has been developed to separate the PAHE currents in the Sb 2 Te 3 film. • The photo-induced anomalous Hall conductivity of the Sb 2 Te 3 is much larger than 2DEG. [ABSTRACT FROM AUTHOR]

Inverse spin Hall effect (ISHE) provides an important way to manipulate and detect spin current via spin–orbit coupling. However, it is difficult to distinguish the ISHE of the top and bottom surface states of topological insulators (TIs). Photo-induced inverse spin Hall effect (PISHE) is a powerful tool to investigate the ISHE of the Dirac surface states of TIs. In this work, PISHE of three-dimensional topological insulators Sb 2 Te 3 with a thickness of 7 and 30 quintuple layer (QL) has been investigated. It is revealed that both of the PISHE currents of the top and bottom surface states are observed in the 7-QL and the 30-QL samples. Besides, a model has been developed to separate the PISHE current of the top and bottom surface states. It is found that the PISHE currents of the top and bottom surface states of the Sb 2 Te 3 films almost do not change with temperature in the range of 77 to 300 K. It is demonstrated that the PISHE current changes linearly with light power, which agrees well with the theoretical model. This study provides a method utilizing circularly polarized light to manipulate and detect the ISHE of the top and bottom surface states of three-dimensional topological insulators. • Both of the PISHE currents of the top and bottom surface states are observed in the 7-QL and the 30-QL Sb 2 Te 3 films. • A model has been developed to separate the PISHE current of the top and bottom surface states. • The PISHE currents of the top and bottom surface states of the Sb 2 Te 3 films almost do not change with temperature in the range of 77 to 300 K. [ABSTRACT FROM AUTHOR]