Dynamical Structure Factor for the Alternating Heisenberg Chain: A Linked Cluster Calculation

Abstract

We develop a linked cluster method to calculate the spectral weights of many-particle excitations at zero temperature. The dynamical structure factor is expressed as a sum of exclusive structure factors, each representing contributions from a given set of excited states. A linked cluster technique to obtain high order series expansions for these quantities is discussed. We apply these methods to the alternating Heisenberg chain around the dimerized limit ($\lambda =0$), where complete wavevector and frequency dependent spectral weights for one and two-particle excitations (continuum and bound-states) are obtained. For small to moderate values of the inter-dimer coupling parameter $\lambda$, these lead to extremely accurate calculations of the dynamical structure factors. We also examine the variation of the relative spectral weights of one and two-particle states with bond alternation all the way up to the limit of the uniform chain ($\lambda =1$). In agreement with Schmidt and Uhrig, we find that the spectral weight is dominated by 2-triplet states even at $\lambda =1$, which implies that a description in terms of triplet-pair excitations remains a good quantitative description of the system even for the uniform chain.

26 pages, 17 figures

References in corpus (2)

• Excitations in one-dimensional S=1/2 quantum antiferromagnets
• DMRG Study of Critical Behavior of the Spin-1/2 Alternating Heisenberg Chain

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