Dynamical Structure Factors for Dimerized Spin Systems

TL;DR

This paper investigates the dynamical structure factors of dimerized spin systems, combining theoretical series expansions and neutron scattering experiments to understand excitation spectra in materials like KCuCl_3.

Contribution

It provides detailed higher-order perturbation calculations of excitation energies and spectral weights in dimerized spin systems, accounting for complex unit cell structures.

Findings

Wave vector dependence is modified in higher-order expansions.

Explicit 10th order results for 1D coupled dimers.

Experimental data supports theoretical predictions.

Abstract

We discuss the transition strength between the disordered ground state and the basic low-lying triplet excitation for interacting dimer materials by presenting theoretical calculations and series expansions as well as inelastic neutron scattering results for the material KCuCl_3. We describe in detail the features resulting from the presence of two differently oriented dimers per unit cell and show how energies and spectral weights of the resulting two modes are related to each other. We present results from the perturbation expansion in the interdimer interaction strength and thus demonstrate that the wave vector dependence of the simple dimer approximation is modified in higher orders. Explicit results are given in 10th order for dimers coupled in 1D, and in 2nd order for dimers coupled in 3D with application to KCuCl_3 and TlCuCl_3.