Valleytronics in bulk MoS2 with a topologic optical field

Abstract

The valley degree of freedom^1-4 of electrons in materials promises routes towards energy-efficient information storage with enticing prospects for quantum information processing^5-7. Current challenges in utilizing valley polarization are symmetry conditions that require monolayer structures^8,9 or specific material engineering^10-13, non-resonant optical control to avoid energy dissipation and the ability to switch valley polarization at optical speed. We demonstrate all-optical and non-resonant control over valley polarization using bulk MoS_2, a centrosymmetric material without Berry curvature at the valleys. Our universal method utilizes spin angular momentum-shaped trefoil optical control pulses^14,15 to switch the material's electronic topology and induce valley polarization by transiently breaking time and space inversion symmetry¹⁶ through a simple phase rotation. We confirm valley polarization through the transient generation of the second harmonic of a non-collinear optical probe pulse, depending on the trefoil phase rotation. The investigation shows that direct optical control over the valley degree of freedom is not limited to monolayer structures. Indeed, such control is possible for systems with an arbitrary number of layers and for bulk materials. Non-resonant valley control is universal and, at optical speeds, unlocks the possibility of engineering efficient multimaterial valleytronic devices operating on quantum coherent timescales.