Evidence for two fluids in the ground state of cuprates

TL;DR

This study uses NMR to reveal that in cuprate superconductors, charge carriers form two distinct fluids, with implications for understanding their magnetic and superconducting properties.

Contribution

It provides evidence for two fluids in the ground state of cuprates and discusses how inhomogeneities and disorder affect superconductivity.

Findings

Hole doping rate is family-independent in underdoped samples.

Not all carriers contribute to magnetic or superconducting order.

Weak chemical disorder impacts T_c.

Abstract

We report charge density measurements, using NMR, in the superconducting compound (Ca_{x}La_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_{y}, which has two independent variables x (family) and y (oxygen). For underdoped samples we find the rate at which holes are introduced into the plane upon oxygenation to be family-independent. In contrast, not all carriers contribute to either antiferromagnetic or superconducting order parameters. This result is consistent with a two fluid phenomenology or intrinsic mesoscopic inhomogeneities in the bulk. We also discuss the impact of weak-chemical-disorder on T_{c}.