High Spin Thermoelectricity and Pure Spin Photogalvanic Effects in h -Phase Niobium Dinitride Monolayers and Edge-Engineered Nanoribbons

Based on density functional theory (DFT) and quantum transport simulations, this study systematically investigates the spin-resolved electronic and transport properties of the hydrogenated hexagonal monolayer niobium dinitride (h-phase monolayer NbN2H2) and its corresponding nanoribbons. The monolayer NbN2H2 is identified as a spin semiconductor with a finite spin bandgap of 0.594 eV, exhibiting distinct spin split valence and conduction bands dominated by Nb d-orbitals. In the two-probe configuration of NbN2H2, the system shows significant spin-dependent transmission under parallel magnetic alignment, while transmission is suppressed in the antiparallel configuration. Remarkably, the monolayer exhibits a large spin Seebeck coefficient (∼2236.8 μV/K) and a low charge Seebeck coefficient (∼−717.0 μV/K) in parallel magnetic configuration. Spin-polarized photocurrent under light irradiation enables robust pure spin current generation via the photogalvanic effect in the antiparallel magnetic configuration. Furthermore, nanoribbons tailored along armchair and zigzag directions reveal distinct electronic behaviors: armchair nanoribbons retain a spin semiconducting property near the Fermi level, whereas zigzag nanoribbons display metallic characteristics with spin-polarized transport channels. These findings highlight the potential of NbN2H2-based nanostructures for applications in spintronics, spin caloritronics, and pure spin current optoelectronic nanodevice.