APPEARANCE OF NEW LINES AND CHANGE IN-LINE SHAPE IN THE IR-SPECTRUM OF A NAV2O5 SINGLE-CRYSTAL AT A SPIN-PEIERLS TRANSITION

New lines are observed in the infrared spectrum of a crystal due to un it-cell doubling at a spin-Peierls transition (in NaV2O5). The change in the shape of the spectral lines at the spin-Peierls transition is r ecorded. A contour characteristic of a Fano resonance is observed abov e the transition temperature T-sp and the standard symmetric contour i s observed below T-sp. We attribute this effect to the opening of a ga p in the magnetic-excitation spectrum at the spin-Peierls transition, (C) 1997 American Institute of Physics.