20 - Concentration and temperature-dependence of magnetic polaron spectra in the t–J model

Summary

Abstract

The spectral function and momentum distribution for holes in an antiferromagnet are calculated on the basis of the t–J model in a slave-fermion representation. The self-consistent Born approximation for a two-time Green function is used to study the dependences on temperature and doping (δ) of the self-energy operator. The numerical calculations show weak dependences on concentration and temperature of the spectral function (quasi-particle hole spectrum) while the momentum distribution function changes dramatically with increasing temperature for T>T_d with T_d⋍Jδ.

Introduction

The problem of hole motion in an antiferromagnetic (AF) background has attracted much attention in recent years. That is mainly due to the hope of elucidating the nature of the carriers involved in high-T_c superconductivity in copper oxides. It is believed that the essential features of the problem are described by the t–J model with a Hamiltonian written as

Here 〈ij〉 indicates nearest-neighbor pairs, c⁺_iσ = c⁺_iσ (1 − n_{i − σ}) are the electron operators with the constraint of no double occupancy. The properties of a single hole doped in the Néel spin background have been analyzed intensively with various numerical and analytical methods. Among them are exact diagonalization of small clusters [1] and variational calculations [2]. A rather transparent description within a ‘string’ picture has been developed by several authors [3]. A perturbative approach to the problem was proposed by Schmitt–Rink, Varma and Ruckenstein [4] and developed further by Kane, Lee and Read [5] and Martinez and Horsch [6].