On the Bose-Einstein Condensation of Magnons in Cs2CuCl4

TL;DR

This paper critically examines experimental claims of magnon Bose-Einstein condensation in Cs2CuCl4, arguing that model-dependent uncertainties undermine the interpretation of critical exponents supporting BEC.

Contribution

It demonstrates that the experimental determination of the critical exponent is highly uncertain due to model-dependent errors, challenging previous claims of BEC realization.

Findings

Uncertainty in critical exponent is too large to confirm BEC universality class.

Model-dependent approximations significantly affect the interpretation of experimental data.

Previous claims of BEC in Cs2CuCl4 are overstated due to neglected errors.

Abstract

In a recent paper \cite{Radu}, Radu \textit{et al.} report experimental results they claim to support Bose-Einstein condensation (BEC) of magnons in Cs$_2$CuCl$_4$. It is true that an experimentally measured critical power law scaling exponent in agreement with the BEC universality class would support the realization of a BEC in magnetic systems that order as a canted antiferromagnet. It can be shown, however, that the claim of Radu {\it et al.} is overstated in this instance, because their determination of the critical exponent $\phi$ relies on a model-dependent theoretical approximation to the critical field $H_{\textrm{c1}}$ for which the associated errors are neglected. We show that when these errors are included, the uncertainty in the obtained exponent is so large that the available experimental data cannot be used to differentiate between contending universality classes.