Nonequilibrium magnons from hot electrons in antiferromagnetic systems

TL;DR

This paper introduces a nonthermal mechanism for exciting magnons in antiferromagnetic systems using hot electrons generated by ultrafast laser pulses, enabling control of spin dynamics on ultrafast timescales.

Contribution

It presents a quantum kinetic model for electron-magnon interactions that explains how hot electrons can induce nonequilibrium magnon populations in AFM materials.

Findings

Magnon populations can be excited on a subnanosecond timescale.

External magnetic fields can manipulate nonequilibrium magnon populations.

The mechanism applies to both bulk AFM metals and AFM/normal-metal interfaces.

Abstract

We describe a \emph{nonthermal} magnon activation mechanism in antiferromagnetic (AFM) systems via locally equilibrated \emph{spin-unpolarized} hot electrons excited by an ultrafast intense laser pulse. We employ a quantum kinetic equation that takes into account a direct electron-magnon scattering channel in either bulk AFM metal or at the interface of the AFM/normal-metal heterostructure. The mechanism is responsible for the nonequilibrium population of AFM magnon modes on a subnanosecond timescale, which are formed shortly after the local thermalization of hot electrons by Coulomb interactions. Nonequilibrium magnon populations can be additionally manipulated by applying an external magnetic field. Our work paves the way toward spin dynamics control in AFM systems via the ultrafast manipulation of out-of-equilibrium magnon excitations.