Generation, transport and detection of valley-locked spin photocurrent in WSe2–graphene–Bi2Se3 heterostructures

Abstract

Quantum optoelectronic devices capable of isolating a target degree of freedom (DoF) from other DoFs have allowed for new applications in modern information technology. Many works on solid-state spintronics have focused on methods to disentangle the spin DoF from the charge DoF, yet many related issues remain unresolved. Although the recent advent of atomically thin transition metal dichalcogenides (TMDs) has enabled the use of valley pseudospin as an alternative DoF, it is nontrivial to separate the spin DoF from the valley DoF since the time-reversal valley DoF is intrinsically locked with the spin DoF. Here, we demonstrate lateral TMD-graphene-topological insulator hetero-devices with the possibility of such a DoF-selective measurement. We generate the valley-locked spin DoF via a circular photogalvanic effect in an electric-double-layer WSe transistor. The valley-locked spin photocarriers then diffuse in a submicrometre-long graphene layer, and the spin DoF is measured separately in the topological insulator via non-local electrical detection using the characteristic spin-momentum locking. Operating at room temperature, our integrated devices exhibit a non-local spin polarization degree of higher than 0.5, providing the potential for coupled opto-spin-valleytronic applications that independently exploit the valley and spin DoFs.

Topological insulator metamaterial with giant circular photogalvanic effect

“…where I + and −I − are, respectively, the values of photocurrents under left and right circularly polarized optical excitation, excluding the spin-insensitive component D (44). A threefold increase of the degree of spin polarization of unstructured BSTS ( circ = 0.26) is seen in the BSTS metamaterial ( circ = 0.87), an unprecedented degree of spin polarization approaching unity even at room temperature in nonmagnetic materials (44)(45)(46)(47). Additional validation of the functional dependence of the HDPC on incidence angle  is shown in the Supplementary Materials (section S2 and figs.…”

2D Bi2Se3 materials for optoelectronics

“… (E) Helicity-dependent photocurrent of the heterostructure. (D and E) Reproduced with permission from ( Cha et al., 2018 ). Copyright 2018 Springer Nature.…”

“…Recently, Choi et al. reported a lateral heterostructure opto-spintronic device composed of Bi 2 Se 3 , graphene and WSe 2 for the demonstration of generation, transport and detection of valley-locked spin photocurrent ( Cha et al., 2018 ). In this configuration ( Figure 7 D), the WSe 2 flake was used for the optical generation and electrical regulation of valley-locked spin-polarized carriers, graphene served as the carrier transport channel and Bi 2 Se 3 played the role in detecting spin-polarized carriers.…”

Polarization-Dependent Optical Properties and Optoelectronic Devices of 2D Materials

“…A few works demonstrate the electrical control of CPGE in 2D semiconductors [ 220 , 221 ]. Both of the magnitude and the polarization degree of the photocurrent can be tuned actively, which arises from the spin-valley coupling induced photogenerated carriers.…”