Spin stiffness, spectral weight, and Landau damping of magnons in metallic spiral magnets

TL;DR

This paper investigates the properties of magnons in metallic spiral magnets, deriving their dispersion, spectral weights, and damping rates using a theoretical RPA approach, revealing stable out-of-plane modes despite damping effects.

Contribution

It provides a comprehensive theoretical analysis of magnon excitations, including spin stiffness, spectral weights, and damping, in metallic spiral magnets with a new focus on Landau damping effects.

Findings

Identified three magnon branches with distinct fluctuation characteristics.

Derived general expressions for spin stiffnesses and spectral weights.

Found that out-of-plane magnons are more stable against Landau damping.

Abstract

We analyze the properties of magnons in metallic electron systems with spiral magnetic order. Our analysis is based on the random phase approximation for the susceptibilities of tight binding electrons with a local Hubbard interaction in two or three dimensions. We identify three magnon branches from poles in the susceptibilities, one associated with in-plane, the other two associated with out-of-plane fluctuations of the spiral order parameter. We derive general expressions for the spin stiffnesses and the spectral weights of the magnon modes, from which also the magnon velocities can be obtained. Moreover, we determine the size of the decay rates of the magnons due to Landau damping. While the decay rate of the in-plane mode is of the order of its excitation energy, the decay rate of the out-of-plane mode is smaller so that these modes are asymptotically stable excitations even in the presence of Landau damping.