原子极限下三维Rashba异质结构中非常规Lifshitz转变的多能隙超导性
Multigaps superconductivity at unconventional Lifshitz transition in a 3D Rashba heterostructure at atomic limit
摘要：
原子极限下的多能隙超导3D异质结构（HAL）的临界温度可以通过不同能隙间的接触交换相互作用驱动的形状共振而被放大。$T_C$放大是通过调节Lifshitz跃迁奇异节点附近的费米能级来实现的。最近，人们对反转对称性的破坏产生了很高的兴趣，这导致了线性动量自旋-轨道诱导的自旋分裂，通常被称为Rashba自旋-轨道耦合（RSOC），也在3D层状金属中。然而，在具有RSOC的3D HAL中，在非BCS制度中，在非常规Lifshitz转变附近的多能隙超导性的物理尚不清楚。本工作的关键结果是通过Bogoliubov理论得到超导带隙，通过Dirac方程得到三维电子波函数，通过适当地匹配自旋轨道长度和三维超晶格周期来调节多带隙超导性的可行性。研究发现，当费米能在圆节线附近调谐时，RSOC的存在放大了依赖于k的各向异性能隙函数和临界温度。我们的研究结果提出了一种方法来有效地改变宏观超导体凝聚体上的RSOC的影响，通过调整超晶格调制参数的方式可能相关的自旋电子学功能在几个现有的实验平台和可调材料所需的量子器件的量子计算。
英文摘要：
It is well known that the critical temperature of multi-gap superconducting 3D heterostructures at atomic limit (HAL) made of a superlattice of atomic layers with an electron spectrum made of several quantum subbands can be amplified by a shape resonance driven by the contact exchange interaction between different gaps. The $T_C$ amplification is achieved tuning the Fermi level near the singular nodal point at a Lifshitz transition for opening a neck. Recently high interest has been addressed to the breaking of inversion symmetry which leads to a linear-in-momentum spin-orbit induced spin splitting, universally referred to as Rashba spin-orbit coupling (RSOC) also in 3D layered metals. However the physics of multi-gap superconductivity near unconventional Lifshitz transitions in 3D HAL with RSOC, being in a non-BCS regime, is not known. The key result of this work getting the superconducting gaps by Bogoliubov theory and the 3D electron wave functions by solution of the Dirac equation is the feasibility of tuning multi-gap superconductivity by suitably matching the spin-orbit length with the 3D superlattice period. It is found that the presence of the RSOC amplifies both the k dependent anisotropic gap function and the critical temperature when the Fermi energy is tuned near the circular nodal line. Our results suggest a method to effectively vary the effect of RSOC on macroscopic superconductor condensates via the tuning of the superlattice modulation parameter in a way potentially relevant for spintronics functionalities in several existing experimental platforms and tunable materials needed for quantum devices for quantum computing.
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