Non-reciprocal properties of 2D superconductors
Two-dimensional (2D) superconductors, characterized by their inherent quantum confinement, strong spin-orbit coupling, and diverse forms of symmetry breaking, provide an ideal platform for exploring novel quantum transport phenomena. This review summarizes recent experimental progress in the non-reciprocal properties of 2D superconductors, focusing on second harmonic resistance in the resistive superconducting state and the supercurrent diode effect (SDE) in the dissipationless superconducting regime. We discuss the various origins of these phenomena, distinguishing between intrinsic mechanisms, such as finite-momentum Cooper pairing, and extrinsic mechanisms driven by asymmetric vortex dynamics and device geometry. We present a systematic classification of zero-field SDE into polarity-reversed and polarity-locked behaviors, a distinction governed by the interplay between intrinsic time-reversal symmetry breaking and external magnetic response. Furthermore, we examine how the efficiency and polarity of SDE are modulated by tuning parameters including magnetic/electric fields, strain, device geometry, thermodynamic conditions, and microwave irradiation. We conclude by highlighting the application potential of these tunable diodes in high-efficiency rectification, superconducting logic, and neuromorphic computing.