Pi excitation of the t-J model

TL;DR

This paper analyzes the pi resonance in the t-J model, showing its coupling to spin correlations in superconductors through analytical, numerical, and sum rule approaches, aligning with experimental and theoretical findings.

Contribution

It provides a detailed analysis of the pi resonance in the t-J model, connecting it to spin excitations and SO(5) symmetry, with new calculations and interpretations.

Findings

Pi resonance couples to spin correlations in superconducting state

Results agree with exact diagonalization studies

Energy and momentum dependence matches experimental data

Abstract

In this paper, we present analytical and numerical calculations of the pi resonance in the t-J model. We show in detail how the pi resonance in the particle-particle channel couples to and appears in the dynamical spin correlation function in a superconducting state. The contribution of the pi resonance to the spin excitation spectrum can be estimated from general model-independent sum rules, and it agrees with our detailed calculations. The results are in overall agreement with the exact diagonalization studies of the t-J model. Earlier calculations predicted the correct doping dependence of the neutron resonance peak in the YBCO superconductor, and in this paper detailed energy and momentum dependence of the spin correlation function is presented. The microscopic equations of motion obtained within current formalism agree with that of the SO(5) nonlinear sigma model, where the pi resonance is interpreted as a pseudo Goldstone mode of the spontaneous SO(5) symmetry breaking.