近日，美国麻省理工学院的Zhiyu Dong及其研究小组取得一项新进展。经过不懈努力，他们揭示可调谐载流子波段中库珀对动力学和量子临界超导性的特征
在本研究中，研究人员提出了一种在调整费米曲面几何形状的同时，通过观察超导性的演变来确定运动类型的方法。为了证明其方法的有效性，研究人员利用了最近报道的未扭曲石墨烯多层的相图。他们的分析将费米曲面在不同谷的“幽灵交叉点”的超导性的出现与反向散射类型的对运动学联系起来。
加上观察到的超导性在其开始时的非单调行为（急剧上升然后下降），这为一种特定的量子临界超导性场景提供了强有力的支持，在这种场景中，配对是由谷间相干波动驱动的。这些发现为这些系统中配对的起源提供了直接的见解，为电子-电子相互作用驱动超导性提供了令人信服的证据。更广泛地说，这项工作强调了通过幽灵交叉调谐波段作为提高超导性的有前途的手段的潜力。
据悉，不同的超导配对机制在潜在的库珀对动力学上存在明显的差异。量子临界软模式驱动配对相互作用，其中配对散射过程高度共线，可分为前向散射和后向散射两类。相反，在传统的声子机制中，库珀对散射具有一般的非共线特征。
附：英文原文
Title: Signatures of Cooper pair dynamics and quantum-critical superconductivity in tunable carrier bands
Author: Dong, Zhiyu, Lee, Patrick A., Levitov, Leonid S.
Issue&Volume: 2023-9-22
Abstract: Different superconducting pairing mechanisms are markedly distinct in the underlying Cooper pair kinematics. Quantum-critical soft modes drive pairing interactions in which the pair scattering processes are highly collinear and can be classified into two categories: forward scattering and backscattering. Conversely, in conventional phonon mechanisms, Cooper pair scattering is of a generic noncollinear character. In this study, we present a method to discern the kinematic type by observing the evolution of superconductivity while adjusting the Fermi surface geometry. To demonstrate our approach, we utilize the recently reported phase diagrams of untwisted graphene multilayers. Our analysis connects the emergence of superconductivity at “ghost crossings” of Fermi surfaces in distinct valleys to the pair kinematics of a backscattering type. Together with the observed nonmonotonic behavior of superconductivity near its onset (sharp rise followed by a drop), it lends strong support to a particular quantum-critical superconductivity scenario in which pairing is driven by intervalley coherence fluctuations. These findings offer direct insights into the genesis of pairing in these systems, providing compelling evidence for the electron–electron interactions driving superconductivity. More broadly, our work highlights the potential of tuning bands via ghost crossings as a promising means of boosting superconductivity.
DOI: 10.1073/pnas.2305943120
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2305943120