Dynamical signatures and control of time-reversal breaking in twisted nodal superconductors

TL;DR

This paper investigates the dynamical properties of twisted nodal superconductors, revealing signatures of time-reversal symmetry breaking and proposing experimental detection methods through nonlinear responses and phase transitions.

Contribution

It introduces the concept of a tunable Josephson plasmon mode and links nonlinear dynamical responses to symmetry breaking in twisted superconductors.

Findings

Emergence of a soft collective mode at the time-reversal transition

Second harmonic voltage as a signature of symmetry breaking

Nonlinear driving induces dynamical phase transitions

Abstract

Recent observations of time-reversal breaking superconductivity at twisted cuprate interfaces motivate the development of new approaches to better characterize this emergent phenomenon. Here we study the dynamical properties of the order parameters at the twisted unconventional superconductor interfaces. We reveal the emergence of a soft collective mode (Josephson plasmon) at the time-reversal breaking transition, which can be tuned by temperature, twist angle or magnetic field. Furthermore, nonlinear dynamical responses contain direct signatures of both the transition and the broken symmetry itself. In particular, we show that the generation of a second harmonic voltage under alternating current driving is a necessary and sufficient signature of time-reversal symmetry breaking. Finally, we demonstrate that strong nonlinear driving induces dynamical phase transitions between phases with and without spontaneous symmetry breaking, introducing a tool for their out-of-equilibrium control. We discuss the signatures of our predictions in AC current-driven experiments on twisted Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ interfaces.