Low-energy dimerized Heisenberg antiferromagnet

For a fixed geometry consider a staggered dimerization, that is Si = (—1) . Then we can consider the dimer limit, defined by 0 1 and the weakly-dimerized limit, defined by 0 -C 1. 

2 Weakly dimerized limit 0 -C 1 As the dimerization becomes weaker the two spinons comprising the magnon become less confined, with their 

For most of the parameter range the energy of the first singlet excitation (namely the state), E S = 0), is twice the energy of the lowest triplet. However, as (5 — 0 the singlet becomes a bound bimagnon, as 

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