二维体系中带边位移电流的对称性选择规则
Symmetry selection rule for the band-edge shift current in two dimensions
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中文总结 AI 辅助
该研究揭示二维带隙类狄拉克体系带边位移电流的对称性选择规则，通过三角翘曲调控电流，结合 Bargmann 不变量解释相位相干效应，实现多层石墨烯带边位移电流的栅极切换。
中文摘要 AI 辅助
位移电流是无反演中心晶体的本征体光伏响应。近期计算表明，多层石墨烯中存在大的带边位移电流，该电流在栅极或位移场作用下会反转符号，这一行为无法被量子度量或贝里曲率描述。我们证明该行为遵循对称性原理：在破缺反演的二维带隙类狄拉克体系的吸收边，涌现的低能旋转对称性会抑制该响应；而三角翘曲将该涌现对称性降低为晶格的三重旋转对称性，使电流随翘曲强度线性开启。我们将此表述为精确的角选择规则，统一了多层石墨烯与 kagome 晶格的带边响应。在多带结构中，释放的电流由布洛赫态的带符号、失谐加权的三点 Bargmann 不变量决定：光学振幅保持固定，而 Bargmann 三角形的符号对齐随翘曲增强，这种相位相干效应由有界相干因子描述，无法被包括量子度量在内的任何正定品质因子捕捉。在双层和三层石墨烯中，仅栅极电压即可驱动符号反转，使带边位移电流成为无需参数、可通过栅极切换的体光伏响应。
英文摘要
The shift current is the intrinsic bulk photovoltaic response of a crystal without an inversion center. In graphene multilayers, calculations report large band-edge shift currents that reverse sign under a gate, a behavior that neither the quantum metric nor the Berry curvature captures. We show that this follows from a symmetry principle. At the absorption edge of a gapped, inversion-broken two-dimensional Dirac-like system, an emergent rotational symmetry forbids the response, and the trigonal warping switches it on linearly in its strength, an angular selection rule that unifies multilayer graphene and the kagome lattice. The released current is governed by a signed, detuning-weighted three-point Bargmann invariant: the optical amplitude stays fixed while the sign alignment of the Bargmann triangles grows with the warping, invisible to any positive-definite figure of merit. In bilayer and trilayer graphene the gate alone reverses the sign, making the band-edge shift current a gate-switchable bulk photovoltaic response.
