Quantum damping of skyrmion crystal eigenmodes due to spontaneous quasiparticle decay

Abstract

Skyrmion crystals support chiral magnonic edge states akin to electronic quantum Hall edge states. However, magnonic topology relies on the harmonic approximation, neglecting ubiquitous magnon-magnon interactions that yield a finite zero-temperature quantum damping. We demonstrate that spontaneous quasiparticle decay in two-dimensional ferromagnetic skyrmion crystals is a delicate issue, with the quantum damping ranging over several orders of magnitude. Flat magnon bands cause exceptionally strong spontaneous decay at twice their energy. The resulting externally controllable energy-selective magnon breakdown is measurable not only by scattering but also by magnetic resonance experiments, probing the magnetically active anticlockwise, breathing, and clockwise modes. They exhibit distinct decay behavior, with the clockwise (anticlockwise) mode being the least (most) stable mode out of the three. The quantum damping of the topologically nontrivial anticlockwise mode is negligible, establishing the harmonic theory as a trustworthy approximation at low energies, implying excellent prospects of topological magnonics in skyrmion crystals.

Laser-controlled real- and reciprocal-space topology in multiferroic insulators

“…1(a)] where, unlike previous proposals, there is no need to tune the laser frequency to be at resonance with internal skyrmion magnon modes [24,25]. The magnon bands supported by a static skyrmion crystal can also be topological in reciprocal space [26][27][28][29][30][31]. We show that a topological phase transition in the Floquet magnon spectrum can be driven by a terahertz laser [see Fig.…”

Hybrid quantum systems based on magnonics

“…prepared 88,159,160 . More interestingly, topological magnons, chiral magnonic edge state, as well as hybrid and quantum magnonic phenomena were predicted in SMCs in recent works [92][93][94][95][96][97][98]103,106 . According to the spatial dimension of the periodical skyrmion arrangement, SMCs can be classified into two types: 1D-SMCs [88][89][90][91] and 2D-SMCs 92-99 .…”

“…However, the study of quantum magnonic phenomena in SMCs is still lacking. In 2020, A. Mook et al reported a new theoretical study on a quantum-mechanical many-body phenomenon of propagating magnons in SMCs which is called spontaneous quasiparticle decay (SQD) 106 . SQD of magnons is a nonlinear magnon scattering process during which a propagating magnon is scattered into two other magnons while the initial magnon mode is close to the flat magnon bands corresponding to the anticlockwise, breathing, or clockwise mode of the skyrmion lattice.…”

“…SMCs are a new style of MCs in which the artificial periodic structures are constituted by skyrmions [88][89][90][91][92][93][94][95][96][97][98][99][100]104,106 . Because the presence, size and site of the skyrmions can be modulated by external effects, for example, external magnetic fields, electric currents, electric fields or spin waves 148,[154][155][156][157][158] , the magnon band structure of SMCs, especially the existence of magnon band gaps, can be modulated by such external effects while operating.…”

“…Thus, the concept of magnonic crystals (MCs) was put forward 61,69,70,[85][86][87] , in which spin waves (or magnons) can be modulated into magnon bands via artificial periodical structures of magnetic properties. In such a new kind of magnetic media, skyrmion based MCs (SMCs) have attracted much attention due to their dynamically tunability, topological nontrivial characteristics, as well as hybrid and quantum phenomena [88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106] . In this review, we will firstly introduce the concepts of MCs and magnetic skyrmion.…”