We study a generalized quantum spin ladder with staggered long range
interactions that decay as a power-law with exponent
\alphaα.
Using large scale quantum Monte Carlo (QMC) and density matrix
renormalization group (DMRG) simulations, we show that this model
undergoes a transition from a rung-dimer phase characterized by a
non-local string order parameter, to a symmetry broken N'eel phase. We
find evidence that the transition is second order. In the magnetically
ordered phase, the spectrum exhibits gapless modes, while excitations in
the gapped phase are well described in terms of triplons – bound states
of spinons across the legs. We obtain the momentum resolved spin dynamic
structure factor numerically and find a well defined triplon band that
evolves into a gapless magnon dispersion across the transition. We
further discuss the possibility of deconfined criticality in this
model.
We study the nature of the excitations of an antiferromagnetic (AFM) Heisenberg chain with staggered long range interactions using the time-dependent density matrix renormalization group method and by means of a multi-spinon approximation. The chain undergoes true symmetry breaking and develops long range order, transitioning from a gapless spin liquid to a gapless ordered AFM phase. The spin dynamic structure factor shows that the emergence of Néel order can be associated to the formation of bound states of spinons that become coherent magnons. The quasiparticle band leaks out from the two-spinon continuum that is pushed up to higher energies. Our physical picture is also supported by an analysis of the behavior of the excitations in real-time.
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