Dynamical signatures of time-reversal breaking at superconductor interfaces

Recent observations of time-reversal breaking superconductivity at twisted cuprate interfaces motivate developing new approaches to better characterize this emergent phase. Here we study the dynamical properties of superconductor flakes with time-reversal breaking at the interface between them. We reveal the emergence of a soft collective mode at the time-reversal breaking transition, which can be tuned by temperature, twist angle or magnetic field. Furthermore, nonlinear dynamical responses are shown to contain direct signatures of both the transition and the broken symmetry itself. Finally, we discuss the effects of explicit time-reversal symmetry breaking on the collective modes and their potential signatures in radio frequency experiments.