Theory of zero-field superconducting diode effect in twisted trilayer graphene
Theory of zero-field superconducting diode effect in twisted trilayer graphene
复制标题
DOI：
10.1088/2053-1583/ac5b16
复制
发表时间：
2022-04-01
期刊：
影响因子：
5.5
通讯作者：
Scheurer, Mathias S.
中科院分区：
文献类型：
--
作者：
Scammell, Harley D.;Li, J. I. A.;Scheurer, Mathias S.
在最近的实验中（Lin et al 2021 arXiv：2112.07841 [cond-mat.str-el]），由镜像对称扭曲三层石墨烯和WSe 2的异质结构承载的超导相显示出在不存在外部磁场的情况下在相反方向上表现出显著不同的临界电流。我们在这里发展了一个微观理论，并分析了零场超导二极管效应的必要条件。考虑到通过邻近效应在三层石墨烯中诱导的自旋-轨道耦合，我们对配对不稳定性和正常态顺序进行分类，并推导出哪些组合与观察到的二极管效应，特别是其场可训练性一致。我们在几种不同的模型，包括系统的全连续模型中进行明确的二极管效应的计算，并照亮二极管效应和有限动量配对之间的关系。我们的理论还提供了一个自然的解释所观察到的符号变化的电流不对称性与掺杂，这可以与一个近似的手征对称性的系统，和增强的横向电阻以上的超导过渡。我们的研究结果不仅阐明了WSe 2上三层石墨烯的丰富物理性质，而且还建立了一种方法来区分自旋轨道耦合石墨烯莫尔系统中各种候选相互作用诱导的订单，因此也可以作为未来实验的指导。
In a recent experiment (Lin et al 2021 arXiv:2112.07841 [cond-mat.str-el]), the superconducting phase hosted by a heterostructure of mirror-symmetric twisted trilayer graphene and WSe2 was shown to exhibit significantly different critical currents in opposite directions in the absence of external magnetic fields. We here develop a microscopic theory and analyze necessary conditions for this zero-field superconducting diode effect. Taking into account the spin-orbit coupling induced in trilayer graphene via the proximity effect, we classify the pairing instabilities and normal-state orders and derive which combinations are consistent with the observed diode effect, in particular, its field trainability. We perform explicit calculations of the diode effect in several different models, including the full continuum model for the system, and illuminate the relation between the diode effect and finite-momentum pairing. Our theory also provides a natural explanation of the observed sign change of the current asymmetry with doping, which can be related to an approximate chiral symmetry of the system, and of the enhanced transverse resistance above the superconducting transition. Our findings not only elucidate the rich physics of trilayer graphene on WSe2, but also establish a means to distinguish between various candidate interaction-induced orders in spin-orbit-coupled graphene moire systems, and could therefore serve as a guide for future experiments as well.