Engineering Berry curvature dipole and valley orbital magnetization in 2D materials

Jieun LEE

Berry curvature is a physical quantity intrinsic in some periodic crystals which can give rise to many interesting physical phenomena in solid-state materials. Two-dimensional transition metal dichalcogenides such as MoS2 have non-trivial Berry curvatures at the edges of the conduction band at K and K’ valleys. This feature leads to many interesting valley-dependent phenomena such as the valley optical selection rule and the valley Hall effect. In this talk, we show that by further applying strain to monolayer MoS2 and breaking the 3-fold rotational symmetry of the crystal, the dipole moment of the Berry curvature emerges, giving rise to new quantum geometric phenomena. In particular, by applying an electric field in the direction parallel to the Berry curvature dipole, we found the generation of the valley orbital magnetization on monolayer MoS2 through an optical detection scheme using the scanning Kerr rotation microscopy. By fabricating a flexible monolayer MoS2 transistor with tunable strain, we measured the valley orbital magnetization that depends on the magnitude and direction of strain, which is in excellent agreement with the Berry curvature dipole effect. The dependence of the valley magnetization on the electric field, crystal orientation and carrier doping will also be discussed. 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 in 2D crystals.