Reversal of orbital Hall conductivity and emergence of tunable topological quantum states in orbital Hall insulators

Recent findings indicate that orbital angular momentum (OAM) has the capability to induce the intrinsic orbital Hall effect (OHE), which is characterized by orbital Chern number in the orbital Hall insulator. Unlike the spin-polarized channel in the quantum anomalous Hall insulator, the OAM is valley locked, posing challenges in manipulating the corresponding edge state. Here we demonstrate the sign-reversal orbital Chern number through strain engineering by combing the $k\ifmmode\cdot\else\textperiodcentered\fi{}p$ model and first-principles calculation. Under the manipulation of strain, we observe the transfer of nonzero OAM from the valence band to the conduction band, aligning with the orbital contribution in the electronic structure. Our investigation reveals that electrons and holes with OAM exhibit opposing trajectories, resulting in a reversal of the orbital Hall conductivity. Furthermore, we explore the topological quantum state between the sign-reversible OHE.