Spin quadrupoletronics: moving spin anisotropy around

TL;DR

This paper introduces the concept of spin quadrupoletronics, demonstrating how spin anisotropy can be transferred via spin quadrupole moments, leading to new ways to detect and manipulate impurity spins electrically.

Contribution

It develops a theoretical framework for spin quadrupole transport, including current and continuity equations, and applies it to a high-spin valve system to show novel spin control mechanisms.

Findings

Quadrupole back-action induces spin torques and anisotropic relaxation.

Charge transport can detect impurity spins.

Electric fields can manipulate impurity spins.

Abstract

We show that spin anisotropy can be transferred to an isotropic system by transport of spin quadrupole moment. We derive the quadrupole moment current and continuity equation and study a high-spin valve structure consisting of two ferromagnets coupled to a quantum dot probing an impurity spin. The quadrupole back-action on their coupled spin results in spin torques and anisotropic spin relaxation which do not follow from standard spin current considerations. We demonstrate the detection of the impurity spin by charge transport and its manipulation by electric fields.