Theory of the in-plane anisotropy of magnetic excitations in YBa_{2}Cu_{3}O_{6+y}

TL;DR

This paper proposes that correlation effects near a d-wave Fermi surface deformation cause the observed in-plane anisotropy of magnetic excitations in YBa2Cu3O6+y, explaining experimental neutron scattering results.

Contribution

It introduces a theoretical framework using the bilayer t-J model and slave-boson mean-field theory to explain anisotropic magnetic excitations via dFSD correlations.

Findings

dFSD correlations induce xy-anisotropy in magnetic excitations

Anisotropy is prominent at low doping and high temperatures

Scenario explains anisotropy in both optimally doped and underdoped YBCO

Abstract

A pronounced xy-anisotropy was observed in recent neutron scattering experiments for magnetic excitations in untwinned YBa_{2}Cu_{3}O_{6+y} (YBCO). The small anisotropy of the bare band structure due to the orthorhombic crystal symmetry seems to be enhanced by correlation effects. A natural possibility is that the system is close to a Pomeranchuk instability associated with a d-wave Fermi surface deformation (dFSD). We investigate this possibility in the bilayer t-J model within a self-consistent slave-boson mean-field theory. We show that the dFSD correlations drive a pronounced xy-anisotropy of magnetic excitations at low doping and at relatively high temperatures, providing a scenario for the observed xy-anisotropy in optimally doped as well as underdoped YBCO, including the pseudogap phase.