Moire Bilayers and Heterostructures

The responses of materials to external fields are constrained by their symmetries. In this study, we explore spontaneous symmetry breaking in mesoscopic electronic systems induced by cavity vacuum fields, thereby enabling the emergence of originally prohibited responses. As a pertinent example, we consider orbital gyrotropic Hall and magnetic effects, related respectively to Berry curvature dipole and orbital magnetic moment dipole, in a moiré superlattice embedded in a metallic THz resonator. Employing mean-field computations and exact diagonalization, we demonstrate that many-body interaction induced by cavity vacuum filed results in a spontaneous parity symmetry breaking in the ground state with dual degeneracy. The two degenerate states exhibit contrary orbital gyrotropic responses, which are considerable for experimental detection. Furthermore, the gyrotropic effects are highly tunable by the cavity field polarization and external interlayer bias applied to the moiré superlattice. The cavity-embedded moiré superlattice serves as an advanced platform for exploring and manipulating gyrotropic effects.