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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]

Ultra-thin Bi 2 Se 3 nanoplates with high crystal quality are obtained by chemical vapor deposition (CVD). A giant circular photogalvanic effect (CPGE) has been observed in the ultra-thin Bi 2 Se 3 nanoplates, which is about one order larger than that previously observed in the thick Bi 2 Se 3 nanoplates grown by CVD and that in the thin Bi 2 Se 3 film grown by molecular beam epitaxy. By applying an ionic liquid gate, the CPGE can be effectively tuned. As the gate voltage increases, the magnitude of the CPGE current decreases, suggesting that the CPGE current under zero gate voltage is dominated by surface states rather than the two-dimensional electron gas (2DEG). It is revealed that as the surface roughness of the Bi 2 Se 3 nanoplates increases, the CPGE decreases and finally reverses the sign, indicating the dominant contribution of the CPGE switches from the top surface states to the 2DEG or the bottom surface states. [ABSTRACT FROM AUTHOR]

We introduce a convenient and nondestructive method for the quantitative study of symmetry-related factors in low-dimensional semiconductor structures. By experimentally monitoring the intrinsic valence-bands mixing effect (VBME) and its variation with external strain modulation, together with the application of effective-mass theory, intrinsic shear strain and asymmetric interface conditions can be simultaneously determined in InGaAs/InAlAs superlattices. The observed shear strain is of the order of 10 − 3 . Further analysis reveals that the VBME induced by asymmetric interface conditions is weaker than that induced by intrinsic shear strain. In addition, they exhibit a compensating relationship in the studied superlattices. The proposed method can be generalized for quantitative investigation of symmetry-related factors in many other semiconductor nanostructures in the framework of k ⋅ p perturbation theory. [ABSTRACT FROM AUTHOR]