Spin textures and spin-charge interconversion in two-dimensional trigonal materials

Spin-charge interconversion is a central functionality of spintronics. Using three effective k ⋅ p models, we reveal how spin-charge interconversion is governed by the spin texture of Rashba-type bands, distinguishing systems with opposite-chirality spin-split Fermi contours (conventional Rashba bands) from those with same-chirality contours (unconventional Rashba bands). High-throughput screening of trigonal MX2 monolayers, combined with first-principles and Wannier-based tight-binding calculations, reveals a wide diversity of Fermi-surface spin textures that our models capture near the Brillouin-zone center. We show that the current-induced nonequilibrium spin polarization and relevant spin current are controlled by the group velocity, density of states, and spin texture, leading to pronounced Fermi-level sensitivity. At zeros of nonequilibrium spin polarization, i.e., the energies at which the current-induced nonequilibrium spin polarization vanishes, multiband cancellation suppresses the net Edelstein response and strongly reduces the spin-charge interconversion efficiency, even in the presence of strong spin-orbit coupling. Our results expose the rich landscape of spin textures in noncentrosymmetric two-dimensional (2D) trigonal materials and the subtle, highly nontrivial nature of spin-charge interconversion in realistic systems. The complexity can be explicitly attributed to the interplay of spin-orbit coupling, band-structure details (e.g., multiband effects and anisotropy), and scattering processes, which together govern the efficiency and sign of spin-charge interconversion.