Probing superconducting order in overdoped Ca$_{x}$Y$_{1-x}$Ba$_{2}$Cu$_{3}$O$_{7}$ by neutron diffraction measurements of the vortex lattice

TL;DR

This study uses neutron scattering to investigate how calcium doping affects the vortex lattice and superconducting properties in overdoped cuprates, revealing that the d-wave gap symmetry remains unchanged despite doping-induced disorder.

Contribution

It provides new insights into the vortex lattice structure and superconducting gap symmetry in overdoped Ca-Y-Ba-Cu-O, highlighting the effects of doping on vortex behavior and pairing symmetry.

Findings

Vortex lattice transitions shift to lower fields with doping.

The d-wave superconducting gap symmetry persists despite doping.

Evidence of Pauli paramagnetic effects in high-field vortex behavior.

Abstract

We present small angle neutron scattering studies of the magnetic vortex lattice (VL) in Ca$_{0.04}$Y$_{0.96}$Ba$_{2}$Cu$_{3}$O$_{7}$ up to a field of 16.7 T, and Ca$_{0.15}$Y$_{0.85}$Ba$_{2}$Cu$_{3}$O$_{7}$ up to 25 T. We find that the series of vortex lattice structure transitions have shifted down in field relative to those reported for the undoped compound. We attribute this mainly to the weakening of the 1-D superconductivity in the Cu-O chains by the disorder introduced by doping. The hole doping by calcium is also expected to alter the Fermi velocity and it reduces the upper critical field of the system. The high-field structure of the vortex lattice is similar to recent measurements on the parent compound in fields of 25~T, which indicates that the fundamental \textit{d}-wave nature of the superconducting gap is unchanged by calcium doping. This is corroborated by the temperature dependence of the VL form factor which also shows the same \textit{d}-wave behaviour as observed in other cuprates. We also find evidence of Pauli paramagnetic effects in the field dependence of the VL form factor.