title: Phonon analysis of the S = 1 quantum spin systems Ni(5)Te(4)O(12)X(2) (X = Cl and Br).
abstract: We report our investigations of the electrodynamic response of the S = 1 quantum spin systems Ni(5)Te(4)O(12)X(2) (X = Cl and Br), which develop a magnetic ordered state below 30 K. We measure the optical reflectivity over a broad spectral range extending from the far infrared up to the ultraviolet. Besides identifying the electronic interband transitions, we primarily focus our attention on the lattice dynamics, emphasizing the phonon modes spectrum and its temperature dependence. Our findings do not reveal any direct link between possible structural anomalies and the transition into the magnetically ordered state at low temperatures.
authors.affiliation: Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zürich, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Caimi
authors.forename: L
authors.initials: L
authors.lastname: Degiorgi
authors.forename: H
authors.initials: H
authors.lastname: Berger
authors.forename: L
authors.initials: L
authors.lastname: Forró