论文标题
Euler在扭曲的双层石墨烯中阻塞了库珀配对:列表结节超导性和有限的超流量
Euler Obstructed Cooper Pairing in Twisted Bilayer Graphene: Nematic Nodal Superconductivity and Bounded Superfluid Weight
论文作者
论文摘要
魔法角扭曲的双层石墨烯(MATBG)托有具有非零欧拉数的正常状态近灯带,并显示超导性。在这项工作中,我们研究了非平凡的正常状态拓扑对Intervalley $ c_ {2z} \ Mathcal {t} $的影响 - MATBG中不变的平均库珀配对参数。我们表明,配对阶参数始终可以分为一个微不足道的通道,而欧拉(Euler)在所有仪表中都在正常状态下阻塞通道,从而概括了Chern仪表中先前研究的通道分裂。非零的正常状态欧拉数要求Euler阻塞通道的配对差距函数具有零,而琐碎的通道可以具有不变的配对差距函数。当配对是自发的,我们发现足够主导的Euler用两个零阻塞通道通常会导致淋巴结超导性。在精确的灯泡带的近似值下,我们发现,无论欧拉阻塞通道是否主导,平均零温度的超级流体重量通常从下方界定,从而推广以前衍生的对均匀的S波配对的结合。我们在数值上验证了这些语句的配对,从本地有吸引力的交互中得出。我们的工作表明,欧拉阻塞了库珀配对可能在超导MATBG中起着至关重要的作用。
Magic-angle twisted bilayer graphene (MATBG) hosts normal-state nearly-flat bands with nonzero Euler numbers and shows superconductivity. In this work, we study the effects of the nontrivial normal-state band topology on the intervalley $C_{2z}\mathcal{T}$-invariant mean-field Cooper pairing order parameter in MATBG. We show that the pairing order parameter can always be split into a trivial channel and an Euler obstructed channel in all gauges for the normal-state basis, generalizing the previously-studied channel splitting in the Chern gauge. The nonzero normal-state Euler numbers require the pairing gap function of the Euler obstructed channel to have zeros, while the trivial channel can have a nonvanishing pairing gap function. When the pairing is spontaneously nematic, we find that a sufficiently-dominant Euler obstructed channel with two zeros typically leads to nodal superconductivity. Under the approximation of exactly-flat bands, we find that the mean-field zero-temperature superfluid weight is generally bounded from below, no matter whether the Euler obstructed channel is dominant or not, generalizing the previously-derived bound for the uniform s-wave pairing. We numerically verify these statements for pairings derived from a local attractive interaction. Our work suggests that Euler obstructed Cooper pairing may play an essential role in the superconducting MATBG.