Gapless dispersive continuum in a modulated quantum kagome antiferromagnet

TL;DR

This study reports on a new titanium-based quantum kagome antiferromagnet that exhibits a gapless, dispersive continuum of fractionalized excitations, suggesting a quantum spin liquid state with unique spinon-like dynamics.

Contribution

It introduces a novel titanium fluoride kagome antiferromagnet with no magnetic order down to 1.5 K, expanding the material landscape beyond copper-based systems for quantum spin liquids.

Findings

Dispersive continuum of excitations observed at 1.5 K

Fractionalized spinon-like excitations with quasi-1D dispersion

No magnetic order detected down to 1.5 K

Abstract

The pursuit of quantum spin liquid (QSL) states in condensed matter physics has drawn attention to kagome antiferromagnets (AFM) where a two-dimensional corner-sharing network of triangles frustrates conventional magnetic orders. While quantum kagome AFMs based on Cu$^{2+}$ (3d$^9$, $s=\frac{1}{2}$) ions have been extensively studied, there is so far little work beyond copper-based systems. Here we present our bulk magnetization, specific heat and neutron scattering studies on single crystals of a new titanium fluoride Cs$_8$RbK$_3$Ti$_{12}$F$_{48}$ where Ti$^{3+}$ (3d$^1$, $s = \frac{1}{2}$) ions form a modulated quantum kagome antiferromagnet that does not order magnetically down to 1.5 K. Our comprehensive map of the dynamic response function $S(Q,\hbar\omega)$ acquired at 1.5 K where the heat capacity is T-linear reveals a dispersive continuum emanating from soft lines that extend along (100). The data indicate fractionalized spinon-like excitations with quasi-one-dimensional dispersion within a quasi-two-dimensional spin system.