Layer-valley Hall effect under inversion and time-reversal symmetries

Hall effects have been the central paradigms in modern physics, materials science and practical applications, and have led to many exciting breakthroughs, including the discovery of topological Chern invariants and the revolution of metrological resistance standard. To date, the Hall effects have mainly focused on a single degree of freedom (DoF), and most of them require the breaking of spatial-inversion and/or time-reversal symmetries. Here we demonstrate a new type of Hall effect—layer-valley Hall effect—based on a combined layer-valley DoF characterized by the product of layer and valley indices. The layer-valley Hall effect has a quantum origin arising from the layer-valley contrasting Berry curvature, and can occur in nonmagnetic centrosymmetric crystals with both spatial-inversion and time-reversal symmetries, transcending the symmetry constraints of single DoF Hall effect based on the constituent layer or valley index. Moreover, the layer-valley Hall effect is highly tunable and shows a ‘W’ pattern in response to the out-of-plane electric fields. Additionally, we discuss the potential detection approaches and material-specific design principles of layer-valley Hall effect. Our results demonstrate novel Hall physics and open up exotic paradigms for new research direction of layer-valleytronics that exploits the quantum nature of the coupled layer-valley DoF.