Current-induced re-entrant superconductivity and extreme nonreciprocal superconducting diode effect in a valley-polarized system

The superconducting diode effect (SDE) refers to the nonreciprocity of supercurrents, where amplitudes of critical currents for two opposite directions are unequal. Generally, critical currents exist in both positive and negative directions. It was recently found that an extreme nonreciprocity where two superconducting critical currents are both positive (or negative) appears in the small-twist-angle trilayer graphene [Lin, J.-X. et al., Nat. Phys. 18, 1221 (2022)]. Here we theoretically study the intrinsic SDE in a valley-polarized system and show that depairing currents should be remodulated under the interplay between spontaneous valley polarization and current-induced valley polarization modulation. The remodulation can further lead to the extreme nonreciprocity similar to the experiment and also a new phenomenon called current-induced re-entrant superconductivity where the system enters the superconducting phase twice as the current increases. Our work provides a possible mechanism to explain the emergence of extreme nonreciprocity and opens up new horizons to understand the coexistence of superconductivity and valley ferromagnetism.