Magnon Confinement on the Two-Dimensional Penrose Lattice: Perpendicular-Space Analysis of the Dynamic Structure Factor

TL;DR

This study investigates magnon confinement and dynamic structure factors in two-dimensional quasiperiodic Penrose and Ammann-Beenker lattices, revealing localized magnetic excitations and superconfined antiferromagnons through advanced spin-wave analysis.

Contribution

It introduces a detailed analysis of magnon confinement in 2D quasiperiodic lattices, highlighting the unique antiferromagnon localization and the effects of higher-order quantum interactions.

Findings

Identification of flat and self-similar scattering bands in Penrose and Ammann-Beenker lattices.

Discovery of superconfined antiferromagnons unique to the Penrose lattice.

Splitting of flat scattering bands due to quantum interaction effects.

Abstract

Employing the spin-wave formalism within and beyond the harmonic-oscillator approximation, we study the dynamic structure factors of spin-$\frac{1}{2}$ nearest-neighbor quantum Heisenberg antiferromagnets on two-dimensional quasiperiodic lattices with particular emphasis on a magnetic analog to the well-known confined states of a hopping Hamiltonian for independent electrons on a two-dimensional Penrose lattice. We present comprehensive calculations on the $\mathbf{C}_{5\mathrm{v}}$ Penrose tiling in comparison with the $\mathbf{C}_{8\mathrm{v}}$ Ammann-Beenker tiling, revealing their decagonal and octagonal antiferromagnetic microstructures. Their dynamic spin structure factors both exhibit linear soft modes emergent at magnetic Bragg wavevectors and have nearly or fairly flat scattering bands, signifying magnetic excitations localized in some way, at several different energies in a self-similar manner. In particular, the lowest-lying highly flat mode is distinctive of the Penrose lattice, which is mediated by its unique antiferromagnons confined within tricoordinated sites only, unlike their itinerant electron counterparts involving pentacoordinated as well as tricoordinated sites. Bringing harmonic antiferromagnons into higher-order quantum interaction splits the lowest-lying nearly flat scattering band in two, each mediated by further confined antiferromagnons, which is fully demonstrated and throughly visualized in the perpendicular as well as real spaces. We disclose superconfined antiferromagnons on the two-dimensional Penrose lattice.