Dynamic Stripes and Resonance in the Superconducting and Normal Phases of YBa2Cu3O6.5 Ortho-II Superconductor

TL;DR

This study reveals the coexistence of incommensurate stripe-like spin fluctuations and a strong resonance in YBa2Cu3O6.5, persisting across the superconducting transition and indicating incoherent pairing fluctuations in the normal state.

Contribution

It demonstrates the presence of a persistent resonance and stripe modulations in both superconducting and normal phases, highlighting incoherent pairing fluctuations above Tc.

Findings

Resonance at 33 meV persists above Tc.

Stripe modulations are well-developed below Tc.

Resonance is isotropically polarized, carrying ~2.6% of Cu spin spectral weight.

Abstract

We describe the relation between spin fluctuations and superconductivity in a highly-ordered sample of YBaCu3O6.5 using both polarized and unpolarized neutron inelastic scattering. The spin susceptibility in the superconducting phase exhibits one-dimensional incommensurate modulations at low-energies, consistent with hydrodynamic stripes. With increasing energy the susceptibility curves upward to a commensurate, intense, well-defined and asymmetric resonance at 33 meV with a precipitous high-energy cutoff. In the normal phase, which we show is gapless, the resonance remains surprisingly strong and persists clearly in Q scans and energy scans. Its similar asymmetric spectral form above Tc=59 K suggests that incoherent superconducting pairing fluctuations are present in the normal state. On cooling, the resonance and the stripe modulations grow in well above Tc below a temperature that is comparable to the pseudogap temperature where suppression occurs in local and low-momentum properties. The spectral weight that accrues to the resonance is largely acquired by transfer from suppressed low-energy fluctuations. We find the resonance to be isotropically polarized, consistent with a triplet carrying ~2.6% of the total spectral weight of the Cu spins in the planes.