Magnetic Excitations in the Spin Gap System TlCuCl${}_3$

Abstract

Single-crystal neutron inelastic scattering was performed in order to investigate the magnetic excitations in the spin gap system TlCuCl${}_3$. The constant-$\mathbf{Q}$ energy scan profiles were collected in the $a^{\ast }-c^{\ast }$ plane. Three excitations are observed for $E\le 15$ meV. One of the excitations is identified to be magnetic excitation. The lowest magnetic excitation with $E\sim 0.5$ meV occurs at $\mathbf{Q}=(1,0,1)$, as observed in KCuCl${}_3$. The dispersion relation of the magnetic excitation can be fitted to the dispersion formula derived from the weakly coupled dimer model. The intradimer interaction is evaluated as $J=5.23$ meV, which coincides with the value estimated from the susceptibility data. However, one of the interdimer interactions obtained is so large that the weakly coupled dimer model is broken down.

8 pages, revtex, 10 eps figures