Hole pockets in the t-J model
  We present an exact diagonalization study of the electron momentum distribution n(k) in small clusters of t-J model for different hole concentrations and t/J. Structures in n(k) which were previously interpreted as a `large' Fermi surface are identified as originating from the well known many-body backflow. To obtain reliable information about the true Fermi surface, we focus on the regime t=<J, where the backflow effect is weak and suppress the formation of a bound state by introducing a density repulsion between holes. We find clear signatures of a Fermi surface which, contrary to widespread belief but in agreement with recent photemission experiments and Monte Carlo studies for the Hubbard model, takes the form of small hole pockets. Spin ordering is shown to be irrelevant for this form of the Fermi surface. Comparison of the scaling of n(k) and that of the quasiparticle weight with t/J indicates that these pockets persist also for t>J. 
R. Eder and Y. Ohta (Department of Applied Physics, Nagoya University,   Nagoya, Japan)