Electrical Control of Circular Photogalvanic Spin-Valley Photocurrent in a Monolayer Semiconductor

Abstract

In a monolayer transition metal dichalcogenide (TMDC) that lacks structural inversion symmetry, spin degeneracy is lifted by strong spin–orbit coupling, and a distinctive spin-valley locking allows for the creation of valley-locked spin-polarized carriers with a circularly polarized optical excitation. When excited carriers also have net in-plane momentum, spin-polarized photocurrents can be generated at ambient temperature without magnetic fields or materials. The behavior of these spin-polarized photocurrents in monolayer TMDC remains largely unexplored. In this work, we demonstrate the tuning of spin-valley photocurrent generated from the circularly polarized photogalvanic effect in monolayer MoS2, including magnitude and polarization degree, by purely electric means at room temperature. The magnitude of spin-polarized photocurrent can be modulated up to 45 times larger, and the polarization degree of the total photocurrent can be tuned significantly (here from 0.5 to 16.6%) by gate control. Combined with the atomic thickness and wafer-scale growth capabilities of monolayer TMDC, the efficient electrical tuning of spin-valley photocurrent suggests a pathway to achieve spin-logic processing by local gate architectures in monolayer opto-spintronic devices.

Self-Powered Filterless On-Chip Full-Stokes Polarimeter

“…[22][23][24] The valley-dependent optical selection rule can induce the valley-locked spin-polarized photocurrent which is called circular photogalvanic effect (CPGE). [25][26][27][28] With the aid of CPGE in SL TMDCs, the helicity of the circularly polarized light can be identified. Nevertheless, this effect is usually rather weak and only high-intensity excitation can generate a detectable CPGE current, 25,26,28 which makes it difficult to detect weak circularly polarized light.…”

Light-field and spin-orbit-driven currents in van der Waals materials

“…Photogalvanic effects have been studied extensively for 2D electron gases in III-V semiconductors [89]. Furthermore, they have been applied both experimentally and theoretically to van der Waals materials, including 3D topological insulators [58,59,62,[93][94][95][96][97][98][99], 2D TMDs [17,18,100], WS 2 nanotubes [101], polar van der Waals materials [102,103], and layered Weyl semimetals [104][105][106][107]. Photogalvanic currents form an effective toolbox to explore fundamental optoelectronic symmetries.…”

“…In the monolayer limit, these prototypical TMDs are directgap semiconductors, whose optical properties are dominated by many-body exciton physics, even at room temperature [15,16]. Due to their strong spin-orbit coupling, monolayer TMDs inherently intertwine angular momentum, out-of-plane spin, and crystal momentum degrees of freedom, such that under polarized optical excitation directed spin and charge currents can emerge [17][18][19][20][21]. Directly after a pulsed photoexcitation, the presence of a large density of (photogenerated) charge carriers can alter the Coulomb screening in monolayer TMDs [22][23][24][25][26][27][28][29], such that both the quasi-particle band gap and the excitonic binding energies are renormalized on femtosecond time scales.…”

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

“…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. The amplified photocurrents can be modulated up to 45 times, and the polarization degree of the total photocurrent can be tuned from 0.5% to 16.6% significantly, as shown in Figure 10(a) [ 222 ]. Moreover, the symmetry of the photocurrent has been systematically studied that it can be modulated by the excitation wavelength, the drain-source voltage, and the azimuthal and the incident angle.…”

“…Panel (a) is reproduced with permission from Ref. [ 222 ], copyright 2018 ACS Applied Materials & Interfaces . Panel (b) is reproduced with permission from Ref.…”