Spin-orbit induced equilibrium spin currents in materials
arXiv:2109.03790 · doi:10.1103/PhysRevB.105.024409
Abstract
The existence of spin-currents in absence of any driving external fields is commonly considered an exotic phenomenon appearing only in quantum materials, such as topological insulators. We demonstrate instead that equilibrium spin currents are a rather general property of materials with non negligible spin-orbit coupling (SOC). Equilibrium spin currents can be present at the surfaces of a slab. Yet, we also propose the existence of global equilibrium spin currents, which are net bulk spin-currents along specific crystallographic directions of materials. Equilibrium spin currents are allowed by symmetry in a very broad class of systems having gyrotropic point groups. The physics behind equilibrium spin currents is uncovered by making an analogy between electronic systems with SOC and non-Abelian gauge theories. The electron spin can be seen as the analogous of the color degree of freedom and equilibrium spin currents can then be identified with diamagnetic color currents appearing as the response to an effective non-Abelian magnetic field generated by SOC. Equilibrium spin currents are not associated with spin transport and accumulation, but they should nonetheless be carefully taken into account when computing transport spin currents. We provide quantitative estimates of equilibrium spin currents for several systems, specifically metallic surfaces presenting Rashba-like surface states, nitride semiconducting nanostructures and bulk materials, such as the prototypical gyrotropic medium tellurium. In doing so, we also point out the limitations of model approaches showing that first-principles calculations are needed to obtain reliable predictions. We therefore use Density Functional Theory computing the so-called bond currents, which represent a powerful tool to understand the relation between equilibrium currents, electronic structure and crystal point group.
References in corpus (21)
- Advanced capabilities for materials modelling with Quantum ESPRESSO
- Direct electronic measurement of the spin Hall effect
- Strain gradient induced polarization in SrTiO3 single crystals
- An Exact SU(2) Symmetry and Persistent Spin Helix in a Spin-Orbit Coupled System
- On A Proper Definition of Spin Current
- Weyl Node and Spin Texture in Trigonal Tellurium and Selenium
- Anomalous Bias Dependence of Spin Torque in Magnetic Tunnel Junctions
- Spin-orbit torques in heavy metal/ferromagnet bilayers with varying strength of interfacial spin-orbit coupling
- Imaging mesoscopic spin Hall flow: Spatial distribution of local spin currents and spin densities in and out of multiterminal spin-orbit coupled semiconductor nanostructures
- Non-Abelian gauge field theory of the spin-orbit interaction and a perfect spin filter
- Non-Abelian gauge fields in the gradient expansion: generalized Boltzmann and Eilenberger equations
- Observation of second-harmonic generation induced by pure spin currents
- Equilibrium spin currents in the Rashba medium
- Mechanical measurement of equilibrium spin currents in the Rashba medium
- Calculating spin transport properties from first principles: spin currents
- Duality of the spin and density dynamics for two-dimensional electrons with a spin-orbit coupling
- Current-induced spin polarization at the surface of metallic films: a theorem and an ab initio calculation
- Direct measurement of a pure spin current by a polarized light beam
- Single electron control in n-type semiconductor quantum dots using non-Abelian holonomies generated by spin orbit coupling
- Ab-initio transport across Bismuth Selenide surface barriers
- Spin accumulation from the non-Abelian Aharonov-Bohm effect