Dispersion of the odd magnetic resonant mode in near-optimally doped Bi2Sr2CaCu2O8+d

TL;DR

This neutron scattering study reveals the dispersion of the magnetic resonance mode in slightly overdoped Bi2Sr2CaCu2O8+d, showing similarities to YBa2Cu3O6+x and highlighting the effects of superconducting gap distribution and in-plane anisotropy.

Contribution

First detailed measurement of the dispersion of the magnetic resonance mode in Bi2Sr2CaCu2O8+d, linking it to the superconducting gap distribution and anisotropy.

Findings

Resonance peak exhibits intersecting upward- and downward-dispersing branches.

Magnetic response confined below the gapped Stoner continuum.

Intrinsic energy width relates to superconducting gap distribution.

Abstract

We report a neutron scattering study of the spin excitation spectrum in the superconducting state of slightly overdoped Bi2Sr2CaCu2O8+d system (Tc=87 K). We focus on the dispersion of the resonance peak in the superconducting state that is due to a S=1 collective mode. The measured spin excitation spectrum bears a strong similarity to the spectrum of the YBa2Cu3O6+x system for a similar doping level i.e. x= 0.95-1), which consists of intersecting upward- and downward-dispersing branches. A close comparison of the threshold of the electron-hole spin flip continuum, deduced from angle resolved photo-emission measurements in the same system, indicates that the magnetic response in the superconducting state is confined, in both energy and momentum, below the gapped Stoner continuum. In contrast to YBa2Cu3O6+x, the spin excitation spectrum is broader than the experimental resolution. In the framework of an itinerant-electron model, we quantitatively relate this intrinsic energy width to the superconducting gap distribution observed in scanning tunnelling microscopy experiments. Our study further suggests a significant in-plane anisotropy of the magnetic response.