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arXiv · 2609.37418

Nonlinear optical responses of semiconducting graphene nanoribbons: Strong constraint from a hidden symmetry

Jiawei Ruan·Weichen Tang·Yang-Hao Chan·Chen Hu·Xiaoxun Gong·Steven G. Louie
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Abstract

Nonlinear optical (NLO) responses are powerful tools for probing material structures, as they are highly sensitive to spatial symmetries. For instance, it is well known that having inversion symmetry forbids even-order NLO effects. Here, we show that nonspatial symmetries can also significantly constrain NLO responses. In graphene nanoribbons (GNRs) with bipartite-lattice structures, we identify the approximate bipartite-lattice particle-hole (BLPH) symmetry strongly suppresses even-order NLO effects, even for systems with no inversion symmetry. Importantly, we demonstrate that this approximate symmetry enables the optical generation of nearly pure spin shift currents in ferromagnetic GNRs, with the charge shift currents strongly suppressed. The spin orientation of these photo-induced DC spin currents can be easily tuned by an external magnetic field, providing distinct advantages over previous schemes for generating pure spin shift currents in antiferromagnetic systems. We illustrate our findings using a recently synthesized ferromagnetic Janus GNR. Our results underscore the significance of an overlooked symmetry aspect of NLO responses and highlight magnetic GNRs as promising candidates for spintronic devices.

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Jiawei Ruan, Weichen Tang, Yang-Hao Chan, Chen Hu, Xiaoxun Gong, Steven G. Louie. 2026-09-29. Nonlinear optical responses of semiconducting graphene nanoribbons: Strong constraint from a hidden symmetry. https://arxiv.org/abs/2609.37418

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