Neutron scattering study and analytical description of the spin excitation spectrum of twin-free YBa(2)Cu(3)O(6.6)

TL;DR

This study uses neutron scattering to analyze the magnetic excitation spectrum of twin-free YBa2Cu3O6.6, revealing temperature-dependent anisotropy and dispersion features linked to superconductivity and electronic liquid-crystal states.

Contribution

It provides analytical models for the magnetic susceptibility in YBa2Cu3O6.6, incorporating instrumental resolution effects and revealing detailed temperature-dependent spin excitation features.

Findings

At 70 K, the spectrum shows in-plane anisotropy and a Y-shaped dispersion.

At 5 K, a downward-dispersing resonant mode emerges with weaker anisotropy.

The topology change is linked to competition between superconductivity and electronic liquid-crystal states.

Abstract

We present a comprehensive inelastic neutron scattering study of the magnetic excitations in twin-free YBa(2)Cu(3)O(6.6) (Tc=61 K) for 5 K < T < 290 K. Taking full account of the instrumental resolution, we derive analytical model functions for the magnetic susceptibility chi''(Q,omega) at T = 5 K and 70 K in absolute units. Our models are supported by previous results on similar samples and are valid at least up to excitation energies of omega = 100 meV. The detailed knowledge of chi''(Q,omega) permits quantitative comparison to the results of complementary techniques including angle-resolved photoemission spectroscopy (ARPES), as demonstrated in Dahm et al., Nature Phys. 5, 217, (2009). Based on accurate modeling of the effect of the resolution function on the detected intensity, we determine important intrinsic features of the spin excitation spectrum, with a focus on the differences above and below Tc. In particular, at T = 70 K the spectrum exhibits a pronounced twofold in-plane anisotropy at low energies, which evolves towards fourfold rotational symmetry at high energies, and the relation dispersion is "Y"-shaped. At T = 5 K, on the other hand, the spectrum develops a continuous, downward-dispersing "resonant" mode with weaker in-plane anisotropy. We understand this topology change as arising from the competition between superconductivity and the same electronic liquid-crystal state as observed in YBa(2)Cu(3)O(6.45). We discuss our data in the context of different theoretical scenarios suggested to explain this state.