Room Temperature Electrical Control of Spin and Valley Hall Effect in Monolayer WSe2 Transistors for Spintronic Applications

Abstract

Monolayer transition metal dichalcogenide (TMD) materials have exciting potential for applications in spintronics. Due to the monolayer geometry and strong spin-orbit coupling, they are predicted to have a coupled spin and valley Hall effect (SVHE), where valley-polarized conduction carriers have opposite spin [1, 2, 3]. In this context, WSe2 is an attractive system because of its large valence band spin splitting. Lifetimes of spin and valley polarized carriers in monolayer WSe2 have been measured by pump-probe techniques, yielding values from 0.7 ns to 1 μs at 10 K [4, 5, 6]. Such long lifetimes combined with reasonable mobilities lead to spin-valley accumulation that can be imaged by a laser probe via the magneto-optical Kerr effect (MOKE). Here, we present results on fabricating monolayer WSe2 p-type transistors and spatially mapping out the SVHE using MOKE. The maps show distinct valley channels in the transistor at an elevated temperature of 250 K, and the shape of the diffusion is in agreement with a drift diffusion transport model. We show we can control the SVHE magnitude by controlling the electric field in the transistor, and that the effect can be observed up to room temperature. Our results demonstrate the robustness of the SVHE effect and its potential for spintronic device applications. [1] Mak, K. F., et al. Science 344, 1489-1492 (2014). [2] Xiao, D., et al. PRL 108, 196802 (2012). [3] Lee, J., et al. Nat. Nan. 11, 421-425 (2016). [4] Hsu, W. T., et al. Nat. Comm. 6, 8963 (2015). [5] Song, X., et al. Nano Lett 16, 5010-4 (2016). [6] Kim, J., et al. arXiv:1612.05359 (2016).