Magnon-driven chiral charge and spin pumping and electron-magnon scattering from time-dependent quantum transport combined with atomistic spin dynamics theory

TL;DR

This paper introduces a quantum-classical hybrid framework to study how spin waves in a ferromagnetic nanowire can pump chiral charge and spin currents into attached metals, revealing a nonadiabatic, frequency-dependent mechanism distinct from traditional spin pumping.

Contribution

It presents a novel theoretical approach combining quantum transport and atomistic spin dynamics to analyze magnon-driven chiral charge and spin pumping in ferromagnetic nanostructures.

Findings

Chiral charge and spin currents are pumped by spin waves without bias voltage.

The pumping mechanism is nonadiabatic and frequency-dependent, tied to spin wave propagation.

Single-electron interactions with spin waves are modeled using Lorentzian voltage pulses.

Abstract

Using newly developed quantum-classical hybrid framework, we investigate interaction between spin-polarized conduction electrons and a single spin wave (SW) coherently excited within a metallic ferromagnetic nanowire. When the nanowire hosting SW is attached to two normal metal (NM) leads, with no dc bias voltage applied between them, the SW pumps chiral electronic charge and spin currents into the leads---their direction is tied to the direction of SW propagation and they scale linearly with the frequency of the precession. This is in contrast to: standard pumping by the uniform precession mode with identical spin currents flowing in both directions and no accompanying charge current; or experimentally observed [C.~Ciccarelli et al., Nat. Nanotech. 10, 50 (2014); M.~Evelt et al., Phys. Rev. B 95, 024408 (2017)] magnonic charge pumping which requires spin-orbit coupling spin-orbit coupling. The mechanism behind our prediction is nonadiabaticity due to time-retardation effects---motion of localized magnetic moment affects conduction electron spin in a retarded way, so that it takes a finite time until the electron spin reacts to the motion of the classical vector. Upon injecting dc spin-polarized charge current from the left NM lead, electrons interact with SW where outflowing charge and spin current into the right NM lead are changed due to both scattering off time-dependent potential generated by the SW and superposition with the currents pumped by the SW itself. Using Lorentzian voltage pulse to excite leviton out of the Fermi sea, which carries one electron charge with no accompanying electron-hole pairs and behaves as soliton-like quasiparticle, we describe how a single electron interacts with a single SW.