Theory of helimagnons in itinerant quantum systems

TL;DR

This paper develops a theoretical framework for helimagnons in itinerant chiral magnets, revealing their anisotropic dispersion and providing explicit descriptions and observable predictions for their dynamical properties.

Contribution

It introduces a comprehensive effective theory for helimagnons in both classical and quantum helimagnets, connecting microscopic models to observable spin susceptibilities.

Findings

Helimagnons are propagating modes with anisotropic dispersion.

The theory links microscopic models to measurable dynamical spin susceptibility.

Helimagnons exhibit properties analogous to Goldstone modes in liquid crystals.

Abstract

The nature and effects of the Goldstone mode in the ordered phase of helical or chiral itinerant magnets such as MnSi are investigated theoretically. It is shown that the Goldstone mode, or helimagnon, is a propagating mode with a highly anisotropic dispersion relation, in analogy to the Goldstone mode in chiral liquid crystals. Starting from a microscopic theory, a comprehensive effective theory is developed that allows for an explicit description of the helically ordered phase, including the helimagnons, for both classical and quantum helimagnets. The directly observable dynamical spin susceptibility, which reflects the properties of the helimagnon, is calculated.