The spin-$\frac{1}{2}$ XXZ chain system Cs$_2$CoCl$_4$ in a transverse magnetic field

TL;DR

This study demonstrates that Cs$_2$CoCl$_4$ under a transverse magnetic field effectively realizes a spin-$rac{1}{2}$ XXZ chain, revealing an XY-limit anisotropy and a quantum phase transition at a critical field.

Contribution

It provides experimental validation of the XXZ chain model in Cs$_2$CoCl$_4$ and refines the understanding of its anisotropy and phase transition behavior.

Findings

Cs$_2$CoCl$_4$ realizes the spin-$rac{1}{2}$ XXZ chain in a transverse field.

The system is in the XY-limit with a small anisotropy $J_z/J_ot \\approx 0.12$.

A spin-flop Ising quantum phase transition occurs at approximately 2 T.

Abstract

Comparing high-resolution specific heat and thermal expansion measurements to exact finite-size diagonalization, we demonstrate that Cs$_2$CoCl$_4$ for a magnetic field along the crystallographic b axis realizes the spin-$\frac{1}{2}$ XXZ chain in a transverse field. Exploiting both thermal as well as virtual excitations of higher crystal field states, we find that the spin chain is in the XY-limit with an anisotropy $J_z/J_\perp \approx 0.12$ substantially smaller than previously believed. A spin-flop Ising quantum phase transition occurs at a critical field of $\mu_0 H_b^{\rm cr} \approx 2$ T before around 3.5 T the description in terms of an effective spin-$\frac{1}{2}$ chain becomes inapplicable.