Spinon Excitations in the Quasi-1D S = 1/2 Chain Cs4CuSb2Cl12

TL;DR

This paper reports the discovery of a quasi-one-dimensional quantum spin-liquid state in Cs4CuSb2Cl12, characterized by spinon excitations, a broad temperature stability range, and evidence of a weak spin-Peierls transition.

Contribution

It provides the first experimental observation of a 1D gapless QSL with stable spinon excitations in Cs4CuSb2Cl12, expanding understanding of quantum spin liquids in real materials.

Findings

Identification of spinon excitations above 0.8 K

Large T-linear specific heat contribution

Observation of a weak spin-Peierls transition at 0.7 K

Abstract

The spin-1/2 Heisenberg antiferromagnetic chain is ideal for realizing one of the simplest gapless quantum spin-liquids (QSLs), supporting a many-body ground state whose elementary excitations are fractional fermionic excitations called spinons. Here we report the discovery of such a 1D QSL in Cs4CuSb2Cl12. Compared to previously reported S = 1/2 1D chains, this material possesses a wider temperature range over which the QSL state is stabilized. We identify spinon excitations extending at T > 0.8 K, with a large T-linear contribution to the specific heat, gamma = 31.5(2) mJ mol-1 K-2 which contribute itinerantly to thermal transport up to temperatures as high as T = 35 K. At T = 0.7 K, we find a second-order phase transition, suggesting a weak spin-Peierls transition that is unchanged by a 5 T magnetic field. Cs4CuSb2Cl12 reveals new phenomenology deep in the 1D QSL regime, supporting a gapped QSL phase over a wide temperature range compared to many other experimental realizations.