Inverse spin Hall effect induced by asymmetric illumination of light in topological insulator Bi2Se3

Abstract

Using circularly polarized light is an alternative to electronic ways for spin injection into materials. Spins are injected at a point of the light illumination, and then diffuse and spread radially due to the in-plane gradient of the spin density. This diffusion is converted into a circular charge current by the inverse spin Hall effect (ISHE). With shining the circularly polarized light at asymmetric parts of the sample, such as near edges, we detected this current as a helicity-dependent component in the photocurrent. We present a model for this ISHE based on the experimental results and the finiteelement-method (FEM) simulation of the potential distribution induced by spin injection. Our model shows that the ISHE photocurrent generates an electric dipole at the edge of the sample, causing the measured charge current. The asymmetric lightillumination shown here is a simple way to inject and manipulate spins, opening up a door for novel spintronic devices.

Helicity dependent photoresistance measurement vs. beam-shift thermal gradient

“…Here, we characterize this additional effect, and we find a solution for correcting the results. Our findings are relevant for experiments where the circularly polarized focused beam is used to probe locally the helicitydependent properties [19][20][21][22][23][24]26,29,31,34 , as the thermal gradients create similar signals. Furthermore, for experiments using a fixed circularly polarized beam 18,25,27,28,30,32,33,[36][37][38] , the beam deflection associated to the helicity reversal may slightly modify the illumination conditions and also influence the results.…”

“…It has been shown that circularly polarized 15 light can induce the magnetization reversal 5,16 as well as produce photovoltaic or photoresistive effects 17,18 . The changes of photoresistance [19][20][21][22][23][24][25] or photocurrent 24,[26][27][28][29][30][31][32][33][34][35][36] have been attributed to the interaction between light and spin accumulation. This type of effect appears to be "universal", as it has been observed in semiconductors 24,27 , semimetals 25,37 , topological insulators [29][30][31][32][33][34][35][36] , normal metals 19,20 and even complex metalorganics structure 38 .…”

“…The changes of photoresistance [19][20][21][22][23][24][25] or photocurrent 24,[26][27][28][29][30][31][32][33][34][35][36] have been attributed to the interaction between light and spin accumulation. This type of effect appears to be "universal", as it has been observed in semiconductors 24,27 , semimetals 25,37 , topological insulators [29][30][31][32][33][34][35][36] , normal metals 19,20 and even complex metalorganics structure 38 . However, its magnitude can differ by orders of magnitude even for similar materials and experimental conditions [30][31][32] .…”

“…The anisotropic index of refraction causes a different retardation of the orthogonal light polarizations, creating a relative phase shift that defines the resulting circular polarization. The left hand and right hand circularly polarized light is obtained by varying the angle between the optical axis of the birefringent crystal and the polarization plane of the linearly-polarized input light, either mechanically by rotating a quarter-wave plate (λ/ 4) 22,25,[27][28][29]31,[34][35][36]38 or electrically by applying a high voltage to a photoelastic modulator [19][20][21]23,24,26,30,32,37 . The spin-related signals are extracted from the difference of the results obtained for the two helicities of the circularly polarized light.…”