PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS
Abstract
We investigated the infrared reflectivity of several Mg-and Si-substituted CuGeO3 single crystals. The temperature-dependent b-axis and c-axis optical response is reported. For T < T-SP we detected the activation of zone-boundary phonons along the b axis of the crystal on the pure sample and for 1% Mg and 0.7% Si concentrations. From a detailed analysis of the phonon parameters the redshift of the B-2u mode at 48 cm(-1) is observed and discussed in relation to the soft mode expected to drive the spin-Peierls phase transition in CuGeO3. Moreover, the polarization dependence of a magnetic excitation measured in transmission at 44 cm(-1) has been investigated.
