The dynamical enhancement of Dzyaloshinskii-Moriya interaction in lattice Anderson impurity model

TL;DR

This paper introduces a microscopic mechanism for enhancing Dzyaloshinskii-Moriya interactions in metals with Rashba spin-orbit coupling, using a lattice Anderson impurity model and time-dependent perturbation theory.

Contribution

It demonstrates how non-local hybridization and external fields can significantly amplify Dzyaloshinskii-Moriya interactions in a microscopic model.

Findings

Dzyaloshinskii-Moriya term is initially much smaller than Kondo exchange.

External time-dependent fields can enhance the DM interaction by one to two orders of magnitude.

Effective spin Hamiltonian retains form with time-dependent coefficients, enabling tunability.

Abstract

We propose a new route to generate an interband Dzyaloshinskii-Moriya interaction in metals from solely microscopic perspective. The system consists of conduction band electrons in the presence of the Rashba spin-orbit coupling which are coupled to a $f(d)$-type localized and interacting electrons. The double occupancy in the $f$-band is penalized by a significant Coulomb interaction energy, $U$. When the hybridization between two bands is not strictly local, it leads an alternative pathway to a spin Hamiltonian that may proliferate the formation of Skyrmion textures. The effective spin Hamiltonian is derived using the Schriffer-Wolff perturbation theory. In addition to a Kondo spin exchange interaction between conduction band spins and $f(d)$-band spins, which is denoted as $\vec{s}_m \cdot \vec{S}_n$, the spin Hamiltonian admits a {\bf Dzyaloshinskii-Moriya} spin coupling term, $\vec{s}_m \times \vec{S}_n$. The magnitude of the Dzyaloshinskii-Moriya term is approximately ten to hundred times smaller than that of the Kondo term under physically relevant assumptions. The magnitude of spin coupling terms can be engineered using time-dependent external fields, motivating a generalization to a effective time-dependent Hamiltonian. In this respect, the perturbative derivation is extended to include time-dependent external field using a time-dependent SW transformation. The form of the effective spin Hamiltonian is retained while the spin coupling coefficients gain time dependence. It has been shown that the DM term acquires a new energy scale, which leads to an enhancement of one to two orders of magnitude and makes it comparable to the Kondo coupling.