Magentic-Field Induced Quantum Phase Transition and Critical Behavior in a Gapped Spin System TlCuCl${}_3$

Abstract

Magnetization measurements were performed on TlCuCl${}_3$ with gapped ground state. The critical density and the magnetic phase diagram were obtained. The interacting constant was obtained as $U/k_{\mathrm{B}}=313$ K. The experimental phase boundary for $T<5$ K agrees perfectly with the magnon BEC theory based on the Hartree-Fock approximation with realistic dispersion relations and $U/k_{\mathrm{B}}=320$ K. The exponent $\varphi$ obtained with all the data points for $T<5$ K is $\varphi =1.99$, which is somewhat larger than theoretical exponent ${\varphi }_{\mathrm{BEC}}=3/2$. However, it was found that the exponent converges at ${\varphi }_{\mathrm{BEC}}=3/2$ with decreasing fitting window.

2 pages, 2 figures, Submitted to Proceedings of International Conference on Magnetism (ICM2006)