Parity and time-reversal symmetry breaking in twisted trilayer graphene

By examining the angular dependence of second-harmonic nonlinear response, we report a novel electronic order in twisted trilayer graphene, which is present throughout the entire moire flatband. This is evidenced by a one- or three-fold symmetric angular dependence in the nonreciprocal transport response. By analyzing its dependence on the magnetic field, current flow, and field-effect doping, we show that this parity and time-reversal-breaking order is distinct from the orbital ferromagnetism and nematicity. This discovery has important implications on our fundamental understandings of emergent phenomena in graphene moiré systems, such as the cascade of isospin transitions, superconductivity, nematicity and orbital ferromagnetism.