Spin-orbit induced equilibrium spin currents in materials

The existence of spin-currents in absence any driving external fields is commonly considered an exotic phenomenon appearing only quantum materials, such as topological insulators. We demonstrate instead that equilibrium spin currents are a rather general property materials with non negligible spin-orbit coupling (SOC). Equilibrium can be present at the surfaces slab. Yet, we also propose global currents, which net bulk along specific crystallographic directions materials. allowed by symmetry very broad class systems having gyrotropic point groups. physics behind uncovered making analogy between electronic SOC and non-Abelian gauge theories. electron seen analogous color degree freedom then identified diamagnetic response to effective magnetic field generated SOC. not associated transport accumulation, but they should nonetheless carefully taken into account when computing currents. provide quantitative estimates for several systems, specifically metallic presenting Rashba-like surface states, nitride semiconducting nanostructures prototypical medium tellurium. In doing so, out limitations model approaches showing first-principles calculations needed obtain reliable predictions. therefore use Density Functional Theory so-called bond represent powerful tool understand relation structure crystal group.