Theory of Neutron Scattering in High-T$_c$ Cuprates: Two Component Spin-Fermion Model

TL;DR

This paper introduces a two-component spin-fermion model to explain the magnetic excitation 'hourglass' shape observed in neutron scattering experiments on high-Tc cuprates, combining local spins and itinerant fermions.

Contribution

The paper presents a minimal phenomenological model that captures the magnetic excitation spectrum in high-Tc cuprates, aligning well with experimental data.

Findings

Upward dispersion mainly due to local spins

Downward dispersion from collective fermion excitations

Resonance mode is a mixture of spins and fermions

Abstract

Recent neutron scattering experiments have revealed that the generic form of the magnetic excitations in the high-Tc cuprates of wide range of doping has the so-called "hourglass" shape; it features both upward and downward excitations at the incommensurate (IC) momenta spanning from the resonance peak at the commensurate momentum $(\pi,\pi)$. We propose the two-component spin-fermion model as a minimal phenomenological model which has both local spins and itinerant fermions as independent degrees of freedom. Our calculations of the dynamic spin correlation function provide good agreement with experiments and show: (1) the upward dispersion branch of magnetic excitations is mostly due to the local spin excitations; (2) the downward dispersion branch is from collective spin excitations of fermions; (3) the resonance mode is a mixture of both degrees of freedom.