Two holes in a two-dimensional quantum antiferromagnet: A variational study based on entangled-plaquette states
Abstract
We show that the entangled-plaquette variational ansatz can be adapted to study the two-dimensional t-J model in the presence of two mobile holes. Specifically, we focus on a square lattice comprising up to N=256 sites in the parameter range 0.4≤ J/ t≤2.0. Ground state energies are obtained via the optimization of a wave function in which the weight of a given configuration is expressed in terms of variational coefficients associated with square and linear entangled plaquettes. Our estimates are in excellent agreement with exact results available for the N=16 lattice. By extending our study to considerably larger systems we find, based on the analysis of the long distance tail of the probability of finding two holes at spatial separation r, and on our computed two-hole binding energies, the existence of a two-hole bound state for all the values of J/t explored here. It is estimated that d-wave binding of the two holes does not occur for J/t<Jc/t 0.19.
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