Eur. Phys. J. B 38, 65-70 (2004)
https://doi.org/10.1140/epjb/e2004-00100-7

Infrared spectroscopy of tetrahedral quantum spin systems Cu₂Te₂O₅X₂ (X=Br and Cl)

¹ Laboratorium für Festkörperphysik, ETH Zürich, 8093 Zürich, Switzerland
² Paul Scherrer Institute, 5232 Villigen, Switzerland
³ Department of Physics, EPF Lausanne, 1015 Lausanne, Switzerland
⁴ CNRS, Centre d'élaboration de matériaux et d'études structurales, 31055 Toulouse, France

Corresponding author: ^a degiorgi@solid.phys.ethz.ch

Received: 22 January 2004
Published online: 20 April 2004

Abstract

Cu₂Te₂O₅X₂, with X=Br and Cl, are spin-tetrahedral systems displaying magnetic ordering at low temperatures. We have performed optical reflectivity measurements over a broad spectral range as a function of temperature and magnetic field. We have identified the resonance frequencies of the infrared optically active phonon modes and estimated the value of the electronic gap in both tellurate compounds. No variation of the spectra has been observed while crossing the magnetic ordering transition temperature or by applying a magnetic field. The implications of these findings are discussed in relation to the nature of the phase transition.