Substitution effects on spin fluctuations in the spin-Peierls compound CuGeO_3

TL;DR

This study investigates how chemical substitutions affect spin fluctuations and the spin-Peierls state in CuGeO_3 using Raman scattering, revealing suppression of the spin-Peierls gap and a dimensional crossover below the transition temperature.

Contribution

It provides new insights into how Zn and Si substitutions suppress the spin-Peierls state and alter spin dynamics in CuGeO_3, highlighting the role of spin-lattice interactions.

Findings

Substitutions quench the spin-Peierls state.

Suppression of the spin-Peierls gap below T_{SP}=14K.

Evidence of a dimensional crossover below T_{SP}.

Abstract

Using Raman scattering we studied the effect of substitutions on 1D spin fluctuations in CuGeO_3 observed as a spinon continuum in frustration induced exchange scattering. For temperatures below the spin-Peierls transition (T_{SP}=14K) the intensity of this continuum at 120-500 cm^{-1} is exponentially suppressed and transferred into a 3D two-magnon density of states. Besides a spin-Peierls gap-induced mode at 30 cm^{-1} and additional modes at 105 and 370 cm^{-1} are observed. Substitution of Zn on the Cu-site and Si on the Ge-site of CuGeO_3 quenches easily the spin-Peierls state. Consequently a suppression of the spin-Peierls gap observable below T_{SP}=14K as well as a change of the temperature dependence of the spinon continuum are observed. These effects are discussed in the context of a dimensional crossover of this compound below T_{SP} and strong spin-lattice interaction.