The critical current of a superconductor can be different for opposite directions of current flow when both time-reversal and inversion symmetry are broken. Such non-reciprocal behaviour creates a superconducting diode and has recently been experimentally demonstrated by breaking these symmetries with an applied magnetic field or by the construction of a magnetic tunnel junction. Here we report an intrinsic superconducting diode effect that is present at zero external magnetic field in mirror-symmetric twisted trilayer graphene. Such non-reciprocal behaviour, with sign that can be reversed through training with an out-of-plane magnetic field, provides direct evidence of the microscopic coexistence between superconductivity and time-reversal symmetry breaking. In addition to the magnetic-field trainability, we show that the zero-field diode effect can be controlled by varying the carrier density or twist angle. A natural interpretation for the origin of the intrinsic diode effect is an imbalance in the valley occupation of the underlying Fermi surface, which probably leads to finite-momentum Cooper pairing and nematicity in the superconducting phase.

当时间反转和反转对称性都被破坏时，超导体的临界电流对于电流流动的相反方向可能是不同的。这种非互易行为产生了超导二极管，并且最近通过使用施加的磁场或通过构造磁隧道结来打破这些对称性进行了实验证明。在这里，我们报告了一种内在的超导二极管效应，这种效应存在于镜像对称扭曲三层石墨烯中的零外部磁场。这种非互易行为，其符号可以通过平面外磁场的训练来逆转，为超导性和时间反转对称性破坏之间的微观共存提供了直接证据。除了磁场可训练性，我们表明，可以通过改变载流子密度或扭转角来控制零场二极管效应。对固有二极管效应起源的自然解释是下伏费米表面的谷占据不平衡，这可能导致超导相中的有限动量库珀配对和向列性。