Exotic Spin Excitation Continuum in a Weakly Coupled Quantum Chainsaw Antiferromagnet

TL;DR

This study reveals a continuum of fractionalized spin excitations in a weakly coupled quantum antiferromagnet, demonstrating persistent one-dimensional criticality within a two-dimensional lattice due to anisotropic interactions.

Contribution

It uncovers how directional fractionalized excitations can exist in a quasi-two-dimensional system, linking one-dimensional criticality with higher-dimensional quantum disorder.

Findings

Observation of a broad magnetic excitation continuum in neutron scattering.

Detection of rod-like scattering indicating quasi-one-dimensional correlations.

Evidence of persistent fractionalized excitations within a two-dimensional lattice.

Abstract

Collective motions in strongly interacting magnets involve many spins and are often described in terms of integer-spin excitations. However, in certain cases, the collective motion can behave as if these integer excitations break apart into smaller, particle-like entities with unusual properties. Such fractionalized excitations in quantum magnets are commonly associated either with topological order in two dimensions or with criticality in one dimension. It remains unclear how these distinct mechanisms are connected across a dimensional crossover. Here we investigate the Ti-based quantum antiferromagnet, $Cs_{8}LiNa_{3}Ti_{12}F_{48}$, in which $Ti^{3+}$ ($3d^{1}$, $S=1/2$) ions interact antiferromagnetically within distorted kagome planes. Our inelastic neutron scattering study on a single crystal reveals a frustrated network of weakly coupled spin-$1/2$ chainsaws, realizing a regime of dimensional frustration in which interchain couplings fail to establish coherent two-dimensional order. The magnetic excitation spectrum exhibits a strong continuum spanning the full measured momentum and energy phase space. In addition, the dynamic spin correlation function displays rod-like scattering in momentum space, indicating a quasi-one-dimensional nature of the magnetic correlations. These results point to fractionalized excitations with intrinsically directional character, demonstrating that signatures of one-dimensional criticality can persist within a two-dimensional lattice. Our findings establish anisotropic fractionalization as a distinct organizing principle for quantum-disordered states.