The superconducting diode effect (SDE), characterized by a nonreciprocal critical current $Jc(\hat{n))≠Jc(−\hat{n})$, requires the breaking of inversion and time-reversal symmetry. While symmetry conditions are well established, explaining large current asymmetries in junction-free systems remains challenging.
We investigate two distinct mechanisms for the SDE. First, we show that when time-reversal symmetry is spontaneously broken, the associated order parameter can couple directly to the (super)current. Within phenomenological, microscopic, and time-dependent Ginzburg–Landau approaches, this coupling leads to sizeable current asymmetries and rich non-equilibrium effects arising from the interplay of superconducting, resistive, and symmetry-breaking currents.
Second, we demonstrate that altermagnetism provides an alternative route to nonreciprocal superconductivity. Depending on the crystalline point group and magnetic symmetry, altermagnetic order can generate and control the SDE, with symmetry-pinned or electrically tunable current asymmetry.
Together, these results identify distinct pathways toward realizing and controlling nonreciprocal superconductivity in crystalline systems.