Nonlinear Hall effects in strained twisted bilayer WSe2

Recently, it has been pointed out that the twisting of bilayer WSe2 would generate topologically non-trivial flat bands near the Fermi energy. In this work, we show that twisted bilayer WSe2 (tWSe(2)) with uniaxial strain exhibits a large nonlinear Hall (NLH) response due to the non-trivial Berry curvatures of the flat bands. Moreover, the NLH effect is greatly enhanced near the topological phase transition point which can be tuned by a vertical displacement field. Importantly, the nonlinear Hall signal changes sign across the topological phase transition point and provides a way to identify the topological phase transition and probe the topological properties of the flat bands. The strong enhancement and high tunability of the NLH effect near the topological phase transition point renders tWSe(2) and related moire materials available platforms for rectification and second harmonic generations. The nonlinear Hall effect describes a recently discovered phenomenon in which a time-reversal symmetric material with a Berry curvature dipole develops a transverse voltage at double the frequency of an applied current. Here, the authors theoretically explore twisted bilayer WSe2 under strain, and find that it can exhibit a large nonlinear Hall effect that is highly sensitive to the topological properties of the material.