Charge correlations in the weakly doped t-J model calculated by projection technique

TL;DR

This paper investigates charge correlations in weakly doped antiferromagnets using the t-J model and Mori-Zwanzig projection, revealing insights into charge-density response and optical conductivity consistent with numerical methods.

Contribution

It applies a cumulant formalism with a projection technique to analyze charge correlations in the t-J model, providing results aligned with exact diagonalization.

Findings

Charge-density response shows a broad continuum at energies of several t.

Optical conductivity is dominated by low-energy excitations at 1.5-2 J.

Weak-doping properties are explained by transitions between spin-bag quasiparticle states.

Abstract

We study frequency- and wave-vector dependent charge correlations in weakly doped antiferromagnets using Mori-Zwanzig projection technique. The system is described by the two-dimensional t-J model. The ground state is expressed within a cumulant formalism which has been successfully applied to study magnetic properties of the weakly doped system. Within this approach the ground state contains independent spin-bag quasiparticles (magnetic polarons). We present results for the charge-density response function and for the optical conductivity at zero temperature for different values of t/J. They agree well with numerical results calculated by exact diagonalization techniques. The density response function for intermediate and large momenta shows a broad continuum on energy scales of order of several t whereas the optical conductivity for \omega > 0 is dominated by low energy excitations (at 1.5 - 2 J). We show that these weak-doping properties can be well understood by transitions between excited states of spin-bag quasiparticles.