Tunable pure spin current realized by photogalvanic effect in triangulene dimer based nano-devices

The unique magnetic properties of triangulene and its homologues have generated a great deal of interest in recent years. Triangulene dimers, with their magnetic ground states and the detection of singlet-triplet spin excitations, have been synthesized on-surface by Mishra, and shown to be suitable for spintronics applications. In our study, we use first-principles calculations to investigate the photogalvanic effect (PGE) of triangulene dimers based nano-devices. The devices are constructed by two graphene nanoribbon electrodes and a triangulene dimer molecule connected by carbon chains, which has a spatial inversion symmetry. We find that when light irradiation is applied to the device, there are both spin-up and spin-down current induced with the same magnitude and opposite flowing directions. In this case, there is no accompanying charge current, but a finite pure spin current arises. Furthermore, we find that the currents generated by PGE can be tuned by impurity states. When nitrogen atoms are doped into the triangulene dimer molecule, we observe the emergence of impurity states, which supply other electron transition modes and result in a photo-current under different photon energy. Our findings provide a useful insight into the real application of tunable photoelectric carbon-based nano-devices. The PGE properties of triangulene dimers can be applied in the development of efficient spintronics devices.