Abstract of Publication No. 373
N. Cavadini, W. Henggeler,
A. Furrer, K. Krämer, H. U. Güdel, H. Mutka, A. Wildes and P.
Cu2+ magnetic insulators KCuCl3 and TlCuCl3 are unconventional antiferromagnets
of dimer nature. Both assume a quantum disordered singlet ground state,
and show a finite spin excitation gap to triplet states. Despite the lack of classical
Néel order, true three-dimensional magnetic interactions are realized in the above
compounds. Recent inelastic neutron scattering experiments are presented, which
elucidate the nature of triplet modes under this circumstance. Model predictions
around the dimer limit are derived and successfully compared to the observed
dynamic properties. The latter are representative of a large class of gapped quantum
systems, for which a general phase diagram is discussed.