AI 中文总结
研究与铁磁库耦合的平行双量子点约瑟夫森结中的例外点，通过积分引线获非厄米描述，发现自旋相关耗散等产生并可调控EPs，多体宇称分析建立联系，计算的约瑟夫森电流验证相关特性，确立自旋选择性耗散和干涉磁通为控制参数。
AI 中文摘要
我们研究了与耗散库耦合的平行双量子点约瑟夫森结中的例外点（EPs）。通过对引线进行积分，我们得到了一个非厄米博戈留波夫 - 德热纳描述，其中超导相位差和轨道磁通控制着复安德列夫谱。对于与铁磁库相关的自旋相关耗散，结合磁通量，会产生在有限能隙超导引线中持续存在的二阶EPs。此外，磁通调谐可使两个二阶EPs合并为一个三阶EP，其本征值分裂呈现立方根缩放行为。通过多体宇称分析建立了有限能隙行为差异与偶宇称和奇宇称扇区之间光谱关系的联系。最后，从自由能导数和替代模型密度矩阵计算出的约瑟夫森电流在EPs处表现出一致性且保持连续。这些发现确立了自旋选择性耗散和干涉磁通作为超导纳米结构中稳健非厄米奇点的有效控制参数。
英文摘要
We investigate exceptional points (EPs) in a parallel double-quantum-dot Josephson junction coupled to a dissipative reservoir. By integrating out the leads, we obtain a non-Hermitian Bogoliubov-de Gennes description wherein the superconducting phase difference and orbital flux govern the complex Andreev spectrum. For spin-independent dissipation, the second-order EPs identified within the infinite superconducting gap limit are eliminated when the finite superconducting gap is properly incorporated. In contrast, spin-dependent dissipation originating from a ferromagnetic reservoir, in conjunction with magnetic flux, gives rise to second-order EPs that persist in superconducting leads with finite gap. Moreover, flux tuning enables the coalescence of two second-order EPs into a third-order EP, whose eigenvalue splitting exhibits cubic-root scaling behavior. A many-body parity analysis establishes the connection between the contrasting finite-gap behavior and the spectral relationship between the even- and odd-parity sectors. Finally, Josephson currents calculated from both the free-energy derivative and the surrogate-model density matrix demonstrate consistency and remain continuous across the EPs. These findings establish spin-selective dissipation and interferometric flux as effective control parameters for robust non-Hermitian singularities in superconducting nanostructures.
Comments9 pages, 6 figures
