The spin anisotropy of the magnetic excitations in the normal and superconducting states of optimally doped YBa2Cu3O6.9 studied by polarized neutron spectroscopy

TL;DR

This study uses polarized neutron scattering to analyze magnetic excitations in YBa2Cu3O6.9, revealing anisotropic spin responses that change between normal and superconducting states, especially near the resonance energy.

Contribution

It provides detailed polarization-resolved measurements of magnetic excitations in YBa2Cu3O6.9, highlighting anisotropic behavior in the superconducting state not previously characterized.

Findings

Magnetic excitations are present from 10-60 meV with little polarization dependence in the normal state.

Superconducting state shows enhanced magnetic response near the resonance energy.

Local susceptibility becomes anisotropic at low energies, with suppressed c-axis polarized excitations.

Abstract

We use inelastic neutron scattering with spin polarization analysis to study the magnetic excitations in the normal and superconducting states of YBa2Cu3O6.9. Polarization analysis allows us to determine the spin polarization of the magnetic excitations and to separate them from phonon scattering. In the normal state, we find unambiguous evidence of magnetic excitations over the 10-60meV range of the experiment with little polarization dependence to the excitations. In the superconducting state, the magnetic response is enhanced near the "resonance energy" and above. At lower energies, 10<E<30meV, the local susceptibility becomes anisotropic, with the excitations polarized along the c-axis being suppressed. We find evidence for a new diffuse anisotropic response polarized perpendicular to the c-axis which may carry significant spectral weight.