Zero-field superconducting diode effect in small-twist-angle trilayer graphene

By Jiangxiazi Lin, Phum Siriviboon, H. Scammell, Song Liu, D. Rhodes, K. Watanabe, T. Taniguchi, James C. Hone, M. Scheurer, J.I.A. Li. Nature Physics, 2021

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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. 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.

Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/d2f57a02691b9aa9a1ea00c811d071866509ca69