Dark discrete breather modes in monoaxial chiral helimagnet with easy-plane anisotropy

TL;DR

This paper demonstrates the existence of dark discrete breather modes in a monoaxial chiral helimagnet with easy-plane anisotropy, revealing their stability, energy dependence, and potential for spintronic applications.

Contribution

It introduces dark discrete breather modes in CrNb₃S₆, showing their stability and properties, which is a novel finding in chiral helimagnets with easy-plane anisotropy.

Findings

Dark breather modes are stable and exist within the linear spin-wave band.

Energy decreases linearly with increasing kink number.

Breather properties depend on lattice period and amplitude.

Abstract

Nonlinearity and discreteness are two pivotal factors for an emergence of discrete breather excitations in various media. We argue that these requirements are met in the forced ferromagnetic phase of the monoaxial chiral helimagnet CrNb$_3$S$_6$ due to specific domain structure of the compound. The stationary, time-periodic breather modes appear as the discrete breather lattice solutions whose period mismatches with a system size. Thanks to easy-plane single-ion anisotropy intrinsic to CrNb$_3$S$_6$, these modes are of the dark type with frequencies lying within the linear spin-wave band, close to its bottom edge. They represent cnoidal states of magnetization, similar to the well-known soliton lattice ground state, with differing but limited number of embedded $2\pi$-kinks. Linear stability of these dark breather modes is verified by means of the Floquet analysis. Their energy controlled by two parameters, namely the breather lattice period and amplitude, falls off linearly with a growth of the kink number. These results may pave a new path to design spintronic resonators on the base of chiral helimagnets.