AI 中文总结
研究PT对称二维异质结构中体光伏效应，开发非阿贝尔公式描述其对称简并能带。发现奈尔矢量方向控制拓扑相和光学响应，该结构可产生纯自旋光电流，揭示非线性自旋输运对拓扑和磁对称性的探测作用。
AI 中文摘要
我们研究了由拓扑绝缘体与d波交变磁体耦合而成的PT对称二维异质结构中的体光伏效应（BPVE）。为描述该系统的对称强制简并能带，我们开发了自旋BPVE的非阿贝尔公式，将传统理论从孤立非简并能带扩展到PT简并流形。我们表明，奈尔矢量的方向控制拓扑相和非线性光学响应的特性。当奈尔矢量位于xy平面时，异质结构实现了由C4zT对称保护的二阶拓扑绝缘体（SOTI）。该系统还保留C2z对称，完全抑制二阶电荷光电流，同时允许有限的自旋光电流。结果，BPVE成为本征纯自旋光伏效应，产生无伴随电荷电流的直流自旋电流。我们发现线偏振光驱动自旋转移电流，圆偏振光产生自旋注入电流。每当局部狄拉克质量改变符号时，两种响应都会发生符号反转。随着奈尔矢量向z轴旋转，SOTI相转变为一阶拓扑绝缘相，导致电荷和自旋光电流共存。我们的结果将PT对称交变磁拓扑绝缘体异质结构确立为产生和控制纯自旋光电流的通用平台，并揭示非线性自旋输运是拓扑和磁对称性的灵敏探针。
英文摘要
We investigate the bulk photovoltaic effect (BPVE) in a $PT$-symmetric two-dimensional heterostructure consisting of a topological insulator coupled to a $d$-wave altermagnet. To describe the symmetry-enforced degenerate bands of this system, we develop a non-Abelian formulation of the spin BPVE, extending the conventional theory from isolated nondegenerate bands to $PT$-degenerate manifolds. We show that the orientation of the Néel vector controls both the topological phase and the character of the nonlinear optical response. When the Néel vector lies in the $xy$-plane, the heterostructure realizes a second-order topological insulator (SOTI) protected by $C_{4z}T$ symmetry. The system also retains $C_{2z}$ symmetry, which completely suppresses second-order charge photocurrents while allowing finite spin photocurrents. As a result, the BPVE becomes an intrinsically pure spin photovoltaic effect, generating a dc spin current without an accompanying charge current. We find that linearly polarized light drives a spin shift current, whereas circularly polarized light generates a spin injection current. Both responses undergo a sign reversal whenever the local Dirac mass changes sign. As the Néel vector is rotated toward the $z$-axis, the SOTI phase transforms into a first-order topological insulating phase, leading to the coexistence of charge and spin photocurrents. Our results establish $PT$-symmetric altermagnetic topological-insulator heterostructures as a versatile platform for generating and controlling pure spin photocurrents and reveal nonlinear spin transport as a sensitive probe of topology and magnetic symmetry.
Comments22 pages, 11 figures
