Electrical detection of charge-current-induced spin polarization due to spin-momentum locking in Bi2Se3

Abstract

Topological insulators exhibit metallic surface states populated by massless Dirac fermions with spin-momentum locking, where the carrier spin lies in-plane, locked at right angles to the carrier momentum. Here, we show that a charge current produces a net spin polarization via spin-momentum locking in Bi2Se3 films, and this polarization is directly manifested as a voltage on a ferromagnetic contact. This voltage is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current, scales inversely with Bi2Se3 film thickness, and its sign is that expected from spin-momentum locking rather than Rashba effects. Similar data are obtained for two different ferromagnetic contacts, demonstrating that these behaviours are independent of the details of the ferromagnetic contact. These results demonstrate direct electrical access to the topological insulators' surface-state spin system and enable utilization of its remarkable properties for future technological applications.

Topological insulator based spin valve devices: Evidence for spin polarized transport of spin-momentum-locked topological surface states

“…majorana fermions [4,8]), and the expected helical spin-polarized transport makes TI particularly promising for spintronics device applications [4,[9][10][11][12]. While the existence of the spinmomentum-locked TSS in 3D TIs has been established by spin and angle resolved photoemission spectroscopy (spin ARPES) measurements [13][14][15][16][17][18][19], direct demonstration of the spin-helical current (current induced spin polarization) using spin-sensitive transport measurements have been lacking till very recently [20][21][22], even though various different theoretical proposals have been discussed [9][10][11][12]. Previously, the spin valve effect (where a current flows through two ferromagnets (FM) of parallel magnetizations with lower resistance and antiparallel magnetizations with higher resistance) and spin valve devices have been commonly used to study spin transport in various materials (including metals, semiconductors, and graphene) [23][24][25][26][27].…”

Electrical Detection of Spin-Polarized Surface States Conduction in (Bi0.53Sb0.47)2Te3 Topological Insulator

“…It is noted that the HRS and LRS in our voltage hysteresis is shown opposite from that observed in Bi 2 Se 3 ; 30 however, the interpreted spin texture in this way is consistent with the reported spin-resolved APRES data as illustrated in Figure 2b. 14−16 Furthermore, if the electric current direction was flipped to I dc = −2 μA, then the LRS and HRS were also reversed, 30 contact itself due to effects including AMR, tunneling anisotropic magnetoresistance (TAMR) and anomalous Hall effect (AHE). 30,44−46 To further rule out those effects, control experiments have been carried out on another sample without the Al 2 O 3 layer, in which no hysteresis was observed (see Supporting Information S8 and S9).…”

“…The temperature-dependent spin voltage amplitude is plotted in Figure 4b. Overall, the spin signal amplitude decreases as the temperature increases, 30 suggesting that the effective spin polarization of the total current decreases. This could be attributed to the fact that with the temperature increasing: (1) the bulk conduction increases due to thermally activated bulk dopants, so that the relative contribution from the spin-polarized surface states conduction decreases; 48 (2) inelastic scatterings such as phonon scatterings increase so that the spin polarization of surface states conduction also decreases.…”

Probing Two-dimensional (Bi,Sb)2Te3/h-BN Heterostructures Using Complementary S/TEM and Simulation Techniques

“…Because of their momentum-locked surface states, topological insulators (TIs) are emerging as materials that could provide important advances for magnetoelectronic technologies. Already, spin-transfer torque [1], current-induced spin polarization [2,3], and room-temperature spin injection [4] have been demonstrated as phenomena of interest in TI-based devices.To construct high-quality devices, the atomic-scale properties of TIs and their heterostructures must be well characterized. Scanning and conventional transmission electron microscopy (S/TEM) are ideal tools to achieve this.…”

“…Because of their momentum-locked surface states, topological insulators (TIs) are emerging as materials that could provide important advances for magnetoelectronic technologies. Already, spin-transfer torque [1], current-induced spin polarization [2,3], and room-temperature spin injection [4] have been demonstrated as phenomena of interest in TI-based devices.…”