Peierls Dimerization with Non-Adiabatic Spin-Phonon Coupling

TL;DR

This paper investigates the effects of non-adiabatic spin-phonon coupling on the magnetic properties of a frustrated Heisenberg spin chain, emphasizing the importance of dynamic effects for accurately describing the spin-Peierls state.

Contribution

It provides a detailed analysis of the non-adiabatic regime using Lanczos diagonalization, highlighting how dynamic spin-phonon interactions alter magnetic excitations compared to static models.

Findings

Magnetic properties are strongly renormalized by dynamic effects.

Spin triplet excitation gap varies with phonon frequency.

Dynamic effects are essential for accurate spin-Peierls modeling.

Abstract

We study the magnetic properties of a frustrated Heisenberg spin chain with a dynamic spin-phonon interaction. By Lanczos diagonalization, preserving the full lattice dynamics, we explore the non-adiabatic regime with phonon frequencies comparable to the exchange coupling energy which is e.g. the relevant limit for the spin-Peierls compound $CuGeO_3$. When compared to the static limit of an alternating spin chain the magnetic properties are strongly renormalized due to the coupled dynamics of spin and lattice degrees of freedom. The magnitude of the spin triplet excitation gap changes from a strong to a weak dimerization dependence with increasing phonon frequencies implying the necessity to include dynamic effects in an attempt for a quantitative description of the spin-Peierls state.