SPIN GAP AND SPIN-PHONON INTERACTION IN CUGEO3

We study the spin-Peierls transition in CuGeO3 by means of Raman spect roscopy. Improved measurements directly show the opening of the spin-P eierls energy gap below the transition temperature T-SP. A continuous excitation between 30 and 230 cm(-1), including two well-known low-tem perature peaks, is shown to originate from two-magnon excitations with magnons propagating one-dimensionally along the Cu-chains. Spin-phono n interaction inherent to the spin-Peierls state manifests in form of a pronounced Fano lineshape of the low-temperature peak at 107 cm(-1) as well as newly observed magnon-phonon coupled modes. Additional nove l spectral features inherent to the low-temperature phase are reported . Copyright (C) 1996 Published by Elsevier Science Ltd