Zero-field superconducting diode effect in small-twist-angle trilayer graphene
Zero-field superconducting diode effect in small-twist-angle trilayer graphene
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DOI：
10.1038/s41567-022-01700-1
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发表时间：
2022-08-15
期刊：
影响因子：
19.6
通讯作者：
Li, J. I. A.
中科院分区：
文献类型：
--
作者：
Lin, Jiang-Xiazi;Siriviboon, Phum;Li, J. I. A.
在扭曲三层石墨烯中观测到零磁场下的超导二极管效应。这表明时间反演对称性在本质上被打破，进而导致具有非零质心动量的电子之间发生配对。当时间反演对称性和空间反演对称性均被打破时，超导体的临界电流在电流的相反流动方向上会有所不同。这种非互易行为造就了超导二极管，并且最近已通过施加磁场打破这些对称性或构建磁性隧道结在实验中得以证实。在此，我们报道了在镜面对称扭曲三层石墨烯中零外磁场下存在的本征超导二极管效应。这种非互易行为的符号可通过面外磁场的 “训练” 来反转，为超导性与时间反演对称性破缺之间的微观共存提供了直接证据。除了磁场可训练性之外，我们还表明零场二极管效应可通过改变载流子密度或扭转角来调控。对于本征二极管效应起源的一种自然解释是，底层费米面的谷占据不平衡，这很可能导致超导相中的有限动量库珀配对和向列性。
A superconducting diode effect is observed at zero magnetic field in twisted trilayer graphene. This suggests that time-reversal symmetry is intrinsically broken and leads to pairing between electrons with non-zero centre-of-mass momentum.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.