Recently, Prof. ZHENG Xiaohong¡¯s research group in the Institute of Solid State Physics (ISSP) predicted that systems with spatial inversion symmetry in structure and spatial inversion asymmetry in spin density were ideal candidates for pure spin current generation with photogalvanic effect (PGE).
Further investigation shed light on the occurrence of pure spin current which depended neither on photon energy, nor on polarization type or polarization angle of the light.
They found that although no net charge current was produced, there was a hidden directional flow of electrons, with equal number of electrons of different spins flowing in opposite directions, giving rise to pure spin current when studying the current induced by light irradiation in systems with spatial inversion symmetry in structure and spatial inversion asymmetry in magnetism.
The finding provided a fantastic way for generating pure spin current robustly with PGE and was demonstrated in armchair-edged graphene nanoribbons patterned with triangle antidots with zigzag edge.
PGE is a nonlinear optical effect, which is the generation of direct current in systems with broken spatial inversion symmetry under light irradiation, with no need of a bias. Since the first discovery in 1978, it has always been the topic of numerous studies. Investigation has been carried on systematically in traditional semiconductors, attracting extensive attention in the emerging 2D materials. However, it has been long believed that broken spatial inversion symmetry is a prerequisite for the observation of PGE. Thus, basically all the previous PGE studies have been reported only in systems with broken spatial inversion symmetry.
Previous similar schemes was prohibitively difficult in practice when using PGE in systems with broken spatial inversion symmetry where pure spin current could be produced only at a very special photon energy or a special polarization angle. It¡¯s because that broken spatial inversion symmetry must be imposed and one must judiciously adjust device parameters to achieve zero charge current.
The new scheme greatly simplified the device parameters since the automatic pure spin current generation was protected by the spatial inversion symmetry. Most importantly, the idea could be extended to a wide class of anti-ferromagnetic systems with spatial inversion symmetry for pure spin current generation with PGE.
This work was supported by the National Natural Science Foundation of China and the calculations were performed in Center for Computational Science of CASHIPS, the ScGrid of Supercomputing Center, and Computer Network Information Center of Chinese Academy of Sciences.
Link to paper£ºPure spin current generation via photogalvanic effect with spatial inversion symmetry
Figure 1 The structure of the photoelectric device
Figure 2 The generation process of pure spin current under light irradiation.
Figure 3 The spin dependent photocurrents as a function of: (a) photon energy under linearly polarized light; (b) polarization angle ¦È under linearly polarized light; (c) helicity angle ¦Õ under elliptically polarized light.