Hole pairs in a spin liquid: Influence of electrostatic hole-hole repulsion

Laboratoire de Physique Quantique & Unit´e mixte 10 de Recherche CNRS 5626, Universit´e Paul Sabatier, 11 31062Toulouse, France(Submitted for publication on March 1998)The stability of hole bound states in the t−J model including short-range Coulomb interactions isanalyzed using computational techniques on ladders with up to 2×30 sites. For a nearest-neighbors(NN) hole-hole repulsion, the two-holes bound state is surprisingly robust and breaks only when therepulsion is several times the exchange J. At ∼ 10% hole doping the pairs break only for a NN-repulsion as large as V ∼ 4J. Pair-pair correlations remain robust in the regime of hole binding. Theresults support electronic hole-pairing mechanisms on ladders based on holes moving in spin-liquidbackgrounds. Implications in two dimensions are also presented. The need for better estimations ofthe range and strength of the Coulomb interaction in copper-oxides is remarked.PACS numbers: 74.20.-z, 74.20.Mn, 75.25.Dw