Raman scattering in Zn-, Si- and Mg-doped CuGeO 3

Abstract

The dopant-concentration dependence of the folded phonon at 368 cm −1 in the spin-Peierls (SP) system CuGeO 3 has been studied by Raman scattering. With increasing dopant concentration, the Raman spectrum from the folded phonon weakens in intensity and broadens. In the weakly doped samples, the sharp folded phonon is observed at low temperatures, giving evidence for the coexistence of the SP and antiferromagnetic (AF) orders. In the 4% Si-doped sample, a broad Raman band probably reflecting the one-phonon density of states is observed in the AF phase, indicating the existence of the uniform AF phase. In the 2.1% Zn-doped sample, the 368 cm −1 broad peak is superimposed on the broad band. This concentration is near the critical concentration between the dimerized AF and uniform AF phases. The intensity of the folded phonon in the Mg-doped sample is stronger than those in Zn- and Si-doped samples. The luminescence emitted by the phonon cascade process is observed in the 8.1% Mg-doped sample.