Superconducting diode effect and spontaneous symmetry breaking in multi-layer graphen*

The zero-field superconducting diode effect opens a unique window into the nature of the superconducting phase. Nonreciprocity in the critical superconducting transport indicates that inversion and time-reversal symmetries are broken simultaneously. In this talk, I will discuss the potential origin of the zero-field superconducting diode effect in multi-layer graphene structures. We utilize the angle-resolved measurement of transport nonreciprocity in the normal phase to examine the nature of spontaneous symmetry breaking. The angular dependence in both longitudinal and transverse channels offers direct identification that in-plane rotational and inversion symmetries are broken simultaneously in the normal phase. By investigating the interplay between transport nonreciprocity, ferromagnetism, and superconductivity, our findings suggest that the exchange-driven instability in the momentum space plays a key role in the zero-field superconducting diode effect.