Strain Engineering of the Berry Curvature Dipole and Valley Magnetization in Monolayer MoS2

Abstract

The Berry curvature dipole is a physical quantity that is expected to allow various quantum geometrical phenomena in a range of solid-state systems. Monolayer transition metal dichalcogenides provide an exceptional platform to modulate and investigate the Berry curvature dipole through strain. Here we theoretically demonstrate and experimentally verify for monolayer MoS2 the generation of valley orbital magnetization as a response to an in-plane electric field due to the Berry curvature dipole. The measured valley orbital magnetization shows excellent agreement with the calculated Berry curvature dipole which can be controlled by the magnitude and direction of strain. Our results show that the Berry curvature dipole acts as an effective magnetic field in current-carrying systems, providing a novel route to generate magnetization.Berry curvature is central to various topological phenomena observed in solid-state crystals [1], ultracold atoms [2, 3] and photonic architectures [4]. In view of charge transport, its effect has been assumed to be limited to magnetic systems with broken time reversal symmetry as hallmarked by the anomalous Hall effect [5]. Recent theories, however, demonstrated that in nonlinear regime, Hall effect can occur even in time-reversal symmetric systems if they are noncentrosymmetric and possess reduced symmetry (e.g., only one mirror plane) [6,7]. The nonlinear Hall effect has been attributed to the dipole moment formation of the Berry curvature in momentum space. Such Berry curvature dipole widens the scope of Berry curvature effects. It was recently proposed that in transition metal dichalcogenides (TMDs), the Berry curvature dipole may be generated when spatial symmetries of TMDs are lowered by strain [6,8]. This motivates monolayer TMDs as promising materials venue to examine the Berry curvature dipole. As exemplified by ultracold gases, where the in-depth examination of the Berry curvature effects becomes possible through the Berry curvature variation by the optical lattice modulation [2,3], the mechanical tunability of the Berry curvatures in TMDs provides an ideal avenue to explore the Berry curvature dipole.TMDs are noncentrosymmetric two dimensional materials and have two nonequivalent K and K valleys holding the opposite signs of the Berry curvature [9] ( Fig.

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