Anomalous magnetic excitations of cooperative tetrahedral spin clusters.
An inelastic neutron scattering study of Cu2Te2O5X2 (X=Cl, Br) shows strong dispersive modes with large energy gaps persisting far above TN, notably in Cu2Te2O5Br2. The anomalous features: a coexisting unusually weak Goldstone-like mode observed in Cu2Te2O5Cl2 and the size of the energy gaps cannot be explained by existing theories, such as our mean-field or random-phase approximation. We argue that our findings represent a new general type of behavior due to intercluster quantum fluctuations and call for development of a new theoretical approach.
Prsa
K
K
Laboratory for Neutron Scattering, ETH Zürich and Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland. krunoslav.prsa@psi.ch
Rønnow
H M
HM
Zaharko
O
O
Christensen
N B
NB
Jensen
J
J
Chang
J
J
Streule
S
S
Jiménez-Ruiz
M
M
Berger
H
H
Prester
M
M
Mesot
J
J