Spin susceptibility and the pi-excitation in underdoped cuprates

TL;DR

This paper investigates the spin susceptibility and pi-excitation in underdoped cuprates using the slave-boson t--J-model, revealing doping-dependent resonances consistent with experimental observations.

Contribution

It provides a theoretical analysis of spin and pi-excitation spectra in underdoped cuprates, highlighting the role of spin fluctuations and resonance phenomena.

Findings

Resonance peaks in chi'' and pi'' spectra depend on doping levels.

Peak positions align with neutron scattering experiments in underdoped cuprates.

Spin fluctuations primarily cause the low doping resonance peaks.

Abstract

The dynamical spin susceptibility chi'' at wave vector (pi, pi) and the spectrum pi'' of the spin-triplet particle--particle excitation with center of mass momentum (pi, pi) (pi-excitation) are considered in the slave-boson formulation of the t--J-model. Propagators are calculated in a diagrammatic t-matrix approximation in the d-wave superconducting state for a wide doping range. The resulting spectra chi'' and pi'' both show a resonance at a doping dependent energy, in qualitative agreement with recent numerical cluster calculations. In underdoped systems, the peak position is comparable to that found in neutron scattering experiments. The peak in chi'' as well as pi'' is at low doping entirely caused by spin fluctuations, whereas the triplet particle--particle channel does not contribute as a collective mode.