Dynamic Spin Response for Heisenberg Ladders

TL;DR

This paper uses a plaquette basis and renormalization techniques to efficiently analyze the static and dynamic spin properties of 2-leg Heisenberg ladders, achieving results comparable to more computationally intensive methods.

Contribution

It introduces a simple non-interacting multi-plaquette state approach combined with Contractor Renormalization to accurately study large Heisenberg ladders with reduced computational effort.

Findings

Energy/site and gap agree with DMRG results

Most spin response strength is in the lowest triplet level

Many-body effects significantly enhance the spin response

Abstract

We employ the recently proposed plaquette basis to investigate static and dynamic properties of isotropic 2-leg Heisenberg spin ladders. Simple non-interacting multi-plaquette states provide a remarkably accurate picture of the energy/site and dynamic spin response of these systems. Insights afforded by this simple picture suggest a very efficient truncation scheme for more precise calculations. When the small truncation errors are accounted for using recently developed Contractor Renormalization techniques, very accurate results requiring a small fraction of the computational effort of exact calculations are obtained. These methods allow us to determine the energy/site, gap, and spin response of 2x16 ladders. The former two values are in good agreement with density matrix renormalization group results. The spin response calculations show that nearly all the strength is concentrated in the lowest triplet level and that coherent many-body effects enhance the response/site by nearly a factor of 1.6 over that found for 2x2 systems.