Orbital diffusion, polarization and swapping in centrosymmetric metals

TL;DR

This paper develops a comprehensive theory of charge, spin, and orbital diffusion in metals, revealing unique behaviors of orbital angular momentum and introducing the concept of spin-orbit polarization with implications for experimental orbital transport.

Contribution

It presents a novel theoretical framework for orbital diffusion, polarization, and swapping in centrosymmetric metals, highlighting differences from spin and charge transport.

Findings

Orbital diffusivity is much lower than spin or charge diffusivity.

Pure orbital or spin currents can induce longitudinal currents via spin-orbit polarization.

Orbital currents can undergo momentum swapping without spin-orbit coupling.

Abstract

We propose a general theory of charge, spin, and orbital diffusion based on Keldysh formalism. Our findings indicate that the diffusivity of orbital angular momentum in metals is much lower than that of spin or charge due to the strong orbital intermixing in crystals. Furthermore, our theory introduces the concept of spin-orbit polarization by which a pure orbital (spin) current induces a longitudinal spin (orbital) current, a process as efficient as spin polarization in ferromagnets. Finally, we find that orbital currents undergo momentum swapping, even in the absence of spin-orbit coupling. This theory establishes several key parameters for orbital transport of direct importance to experiments.