Persistent Spin Texture and Spin-Orbital Hall Responses on the AgI (110) Surface

Abstract: A systematic investigation of the structural, electronic, and spin-orbital transport properties of the AgI (110) surface is presented using first-principles calculations combined with analytical modelling. The non-centrosymmetric and nonsymmorphic nature of the system gives rise to a robust persistent spin texture (PST), characterized by a unidirectional spin configuration and suppressed spin relaxation, enabling an effectively infinite spin lifetime. Unlike previously reported PST materials, which are predominantly based on chalcogen compounds, this work demonstrates that a halide semiconductor can host PST, thereby significantly expanding the materials platform for spintronic applications. The underlying mechanism is captured using an effective spin-orbit coupled Hamiltonian, which reproduces the anisotropic spin splitting and momentum shift observed in the band structure. This work introduces two new analytical models describing PST and compares them with existing models, offering new perspectives on PST arising from spin-orbit interaction. In addition, the system exhibits sizable intrinsic spin Hall conductivity (SHC) and orbital Hall conductivity (OHC), highlighting its potential for efficient charge-to-spin and charge-to-orbital conversion. The PST is found to be robust against biaxial strain, structural distortion, and multilayer formation, while a vertical electric field breaks the symmetry protection and drives a transition to a Rashba-type spin texture. These findings establish AgI (110) as a promising platform for realizing long-lived spin transport and tunable spin-orbit functionalities in the low-dimensional halide systems.