Electron momentum distribution function in the t-t '-J model

We study the electron momentum distribution function (EMDF) for the two-dim ensional t-t'-J model doped with one hole on finite clusters by the method of twisted boundary conditions. The results quantitatively agree with our a nalytical results for a single hole in the antiferromagnetic background, ba sed on the self-consistent Born approximation (SCBA). Moreover, within the SCBA an anomalous momentum dependence of EMDF is found, pointing to an emer ging large Fermi surface. The analysis shows that the presence of next-near est-neighbor (NNN) hopping terms changes EMDF only quantitatively if the gr ound state (GS) momentum is at (pi/2,pi 2) and qualitatively if the GS mome ntum is shifted to (pi,0). (C) 2000 Elsevier Science B.V. All rights reserv ed.