Three-Dimensional Crystallization of Vortex Strings in Frustrated Quantum Magnets

TL;DR

This paper explores how frustrated exchange interactions in certain quantum magnets can lead to the formation of complex 3D vortex string crystals near the saturation magnetic field, revealing new phases driven by frustration and anisotropy.

Contribution

It introduces the concept of vortex string crystals in 3D frustrated quantum magnets and analyzes their stability and formation near the saturation field.

Findings

Vortex string crystals occur near the saturation field in frustrated quantum magnets.

Degenerate magnon minima lead to complex magnetic ordering.

Symmetric exchange anisotropy stabilizes vortex crystal phases.

Abstract

We demonstrate that frustrated exchange interactions can produce exotic 3D crystals of vortex strings near the saturation field (H=Hsat) of body- and face-centered cubic Mott insulators. The combination of cubic symmetry and frustration leads to a magnon spectrum of the fully polarized spin state (H>Hsat) with degenerate minima at multiple noncoplanar Q vectors. This spectrum becomes gapless at the quantum critical point H=Hsat and the magnetic ordering below Hsat can be formally described as a condensate of a dilute gas of bosons. By expanding in the lattice gas parameter, we find that different vortex crystals span sizable regions of the phase diagrams for isotropic exchange and are further stabilized by symmetric exchange anisotropy.