Central mode and spin confinement near the boundary of the superconducting phase in YBa2Cu3O6.353 (Tc=18 K)

TL;DR

This study maps the low-energy spin spectrum in underdoped YBa2Cu3O6.353, revealing non-coexistence with antiferromagnetism and identifying two fluctuating spin modes with distinct energy scales and correlation lengths.

Contribution

It provides new insights into spin dynamics near the superconducting boundary in YBa2Cu3O6.353, highlighting the presence of a central mode and short-range correlations without long-range order.

Findings

Two spin fluctuation energy scales identified (~2 meV and <0.08 meV)

No coexistence of superconductivity with long-range antiferromagnetic order

Short correlation lengths indicating subcritical fluctuations

Abstract

We have mapped the neutron scattering spin spectrum at low-energies in YBa2Cu3O6.353 (Tc=18 K) where the doping ~0.06 is near the critical value (pc=0.055) for superconductivity. No coexistence with long range ordered antiferromagnetism is found. The spins fluctuate on two energy scales, one a damped spin response with a ~2 meV relaxation rate and the other a central mode with a relaxation rate that slows to less than 0.08 meV below Tc. The spectrum mirrors that of a soft mode driving a central mode. Extremely short correlation lengths, 42+-5 Angstrom in-plane and 8+-2 Angstrom along the c direction, and isotropic spin orientations for the central mode indicate that the correlations are subcritical with respect to any second order transition to Neel order. The dynamics follows a model where damped spin fluctuations are coupled to the slow fluctuations of regions with correlations shortened by the hole doping.