Quantum spin pumping mediated by magnon

TL;DR

This paper presents a theoretical model for quantum spin pumping via magnons at a ferromagnetic insulator and non-magnetic metal interface, highlighting resonance effects and quantum fluctuation enhancement.

Contribution

It introduces a novel quantum spin pumping mechanism mediated by magnons under a time-dependent magnetic field, distinct from classical models.

Findings

Resonance structure in spin transfer torque as a function of frequency

Spin current generation at thermal equilibrium conditions

Enhanced spin pumping via quantum fluctuations

Abstract

We theoretically propose quantum spin pumping mediated by magnons, under a time-dependent transverse magnetic field, at the interface between a ferromagnetic insulator and a non-magnetic metal. The generation of a spin current under a thermal equilibrium condition is discussed by calculating the spin transfer torque, which breaks the spin conservation law for conduction electrons and operates the coherent magnon state. Localized spins lose spin angular momentum by emitting magnons and conduction electrons flip from down to up by absorbing the momentum. The spin transfer torque has a resonance structure as a function of the angular frequency of the applied transverse field. This fact is useful to enhance the spin pumping effect induced by quantum fluctuations. We also discuss the distinction between our quantum spin pumping theory and the one proposed by Tserkovnyak et al.