Dynamics of the Peierls-active phonon modes in CuGeO_3

TL;DR

This paper revisits the spin-Peierls transition in CuGeO_3, showing that the phonon softening depends on specific parameters and aligning theoretical predictions with experimental data, including fluctuation behavior and quantum criticality.

Contribution

It refines the understanding of phonon behavior in CuGeO_3 by applying and extending the Cross and Fischer model, clarifying conditions for phonon softening and predicting a central peak at the transition.

Findings

No phonon softening occurs in CuGeO_3 due to parameter constraints.

The temperature dependence of phonon modes matches experimental observations.

A central peak at T_SP is predicted, indicating critical fluctuations.

Abstract

We reconsider the Cross and Fischer approach to spin-Peierls transitions. We show that a soft phonon occurs only if Omega_0<2.2 T_SP. For CuGeO_3 this condition is not fulfilled and the calculated temperature dependence of the Peierls-active phonon modes is in excellent agreement with experiment. A central peak of a width ~0.2 meV is predicted at T_SP. Good agreement is found between theory and experiment for the pretransitional Peierls-fluctuations. Finally, we consider the problem of quantum criticality in CuGeO_3.