Spin Pumping into Anisotropic Dirac Electrons

TL;DR

This paper theoretically investigates how microwave-induced spin pumping affects anisotropic Dirac electrons at an interface, revealing that Gilbert damping varies with magnetization direction, which can inform on electronic anisotropy.

Contribution

The study formulates the Gilbert damping enhancement due to spin pumping into anisotropic Dirac electrons, providing a theoretical framework for understanding anisotropy effects in such systems.

Findings

Gilbert damping varies with magnetization direction.

Spin pumping can probe electronic anisotropy.

Theoretical model applied to bismuth-based Dirac systems.

Abstract

We study spin pumping into an anisotropic Dirac electron system induced by microwave irradiation to an adjacent ferromagnetic insulator theoretically. We formulate the Gilbert damping enhancement due to the spin current flowing into the Dirac electron system using second-order perturbation with respect to the interfacial exchange coupling. As an illustration, we consider the anisotropic Dirac system realized in bismuth to show that the Gilbert damping varies according to the magnetization direction in the ferromagnetic insulator. Our results indicate that this setup can provide helpful information on the anisotropy of the Dirac electron system.