Hole pockets in the t-J model

TL;DR

This study uses exact diagonalization to analyze the Fermi surface in the t-J model, revealing small hole pockets consistent with experiments, and clarifying the effects of backflow and spin order.

Contribution

It demonstrates that the true Fermi surface consists of small hole pockets in the t-J model, challenging previous interpretations of large Fermi surfaces.

Findings

Fermi surface manifests as small hole pockets.

Backflow effects are responsible for some structures in n(k).

Hole pockets persist for t > J.

Abstract

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.