Scaling of the superfluid density in severely underdoped YBa2Cu3O6+y

TL;DR

This study investigates the relationship between superfluid density, critical temperature, and conductivity in severely underdoped YBa2Cu3O6+y, revealing a scaling law that suggests a transition from a Josephson phase to a more uniform superconducting state.

Contribution

It extends the superfluid density and conductivity scaling relations to extremely underdoped regimes, indicating a possible Josephson phase at low doping levels.

Findings

The scaling relation rho_0/8 ~ 4.4 sigma_dc T_c holds in severely underdoped YBa2Cu3O6+y.

A transition from a Josephson phase to a uniform superconducting state occurs with increased doping.

The scaling law's validity extends over an order of magnitude in doping levels.

Abstract

Recent measurements on extremely-underdoped YBa2Cu3O6+y [Phys. Rev. Lett. 99, 237003 (2007)] have allowed the critical temperature (T_c), superfluid density [rho_0 (T << T_c)] and dc conductivity [sigma_dc (T ~ T_c)] to be determined for a series of electronic dopings for T_c ~ 3 - 17 K. The general scaling relation rho_0/8 ~ 4.4 sigma_dc T_c is observed, extending the validity of both the ab-plane and c-axis scaling an order of magnitude and creating a region of overlap. This suggests that severely underdoped materials may constitute a Josephson phase; as the electronic doping is increased a more uniform superconducting state emerges.