Intermediate-scale theory for electrons coupled to frustrated local-moments

TL;DR

This paper develops an intermediate-temperature theory for electrons interacting with spin fluctuations in frustrated antiferromagnets, revealing anisotropic scattering effects and contrasting quantum spin dynamics with classical phonon behavior.

Contribution

It introduces a detailed model of electron scattering off non-linear spin fluctuations in frustrated magnets, highlighting temperature-dependent anisotropic scattering and a local dynamical spin-response approximation.

Findings

Anisotropic scattering rate along the Fermi surface at intermediate temperatures.

Disappearance of hot-spot anisotropy with increasing temperature.

Contrast between quantum spin fluctuation effects and classical phonon scattering at high temperatures.

Abstract

A classic route for destroying long-lived electronic quasiparticles in a weakly interacting Fermi liquid is to couple them to other low-energy degrees of freedom that effectively act as a bath. We consider here the problem of electrons scattering off the spin fluctuations of a geometrically frustrated antiferromagnet, whose non-linear Landau-Lifshitz dynamics, which remains non-trivial at all temperatures, we model in detail. At intermediate temperatures and in the absence of any magnetic ordering, the fluctuating local-moments lead to a non-trivial angular anisotropy of the scattering-rate along the Fermi surface, which disappears with increasing temperature, elucidating the role of "hot-spots". Over a remarkably broad window of intermediate and high temperatures, the electronic properties can be described by employing a local approximation for the dynamical spin-response. This we contrast with the more familiar setup of electrons scattering off classical phonons, whose high-temperature limit differs fundamentally on account of their unbounded Hilbert space. We place our results in the context of layered magnetic delafossite compounds.