Dispersion of Magnetic Excitations in Superconducting Optimally Doped YBa_2Cu_3O_6.95

TL;DR

This study uses neutron scattering to reveal that magnetic excitations in optimally doped YBa_2Cu_3O_6.95 form dispersive branches converging at the resonance energy, challenging stripe-based models of incommensurate scattering.

Contribution

It demonstrates that the magnetic excitations are dispersive branches converging at the resonance, excluding stripe-based spin wave models as the origin of incommensurate scattering.

Findings

Resonance peak and incommensurate scattering are from dispersive branches.

Two branches converge near 41 meV to form the resonance.

Results exclude vertical incommensurate rods from stripe spin wave models.

Abstract

Detailed neutron scattering measurements of YBa_2Cu_3O_6.95 found that the resonance peak and incommensurate magnetic scattering induced by superconductivity represent the same physical phenomenon: two dispersive branches that converge near 41 meV and the in-plane wave-vector q_af=(pi/a, pi/a) to form the resonance peak. One branch has a circular symmetry around q_af and quadratic downward dispersion from ~41 meV to the spin gap of 33+-1meV. The other, of lower intensity, disperses from ~41 meV to at least 55 meV. Our results exclude a quartet of vertical incommensurate rods in q-w space expected from spin waves produced by dynamical charge stripes as an origin of the observed incommensurate scattering in optimally-doped YBCO.