%0 Journal Article
%T The spin-$\frac{1}{2}$ XXZ chain system Cs$_2$CoCl$_4$ in a transverse magnetic field
%A O. Breunig
%A M. Garst
%A E. Sela
%A B. Buldmann
%A P. Becker
%A L. Bohaty
%A R. M¨šller
%A T. Lorenz
%J Physics
%D 2013
%I arXiv
%R 10.1103/PhysRevLett.111.187202
%X 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.
%U http://arxiv.org/abs/1307.2870v1