Doping-dependent critical Cooper-pair momentum in thin, underdoped cuprate films

TL;DR

This study measures the critical Cooper-pair momentum in thin underdoped cuprate films, revealing a doping-dependent relationship with superfluid density and confirming a universal model prediction.

Contribution

It introduces a low-field inductive technique to measure $p_c$ across various doping levels, demonstrating its proportionality to superfluid density and validating theoretical predictions.

Findings

Critical pair momentum scales with superfluid density.

Doping dependence of $p_c$ matches theoretical models.

Technique enables measurements without high-field complications.

Abstract

We apply a recently-developed low-field technique to inductively measure the critical pair momentum $p_c$ in thin, underdoped films of Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-\delta}$ and Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ reflecting a wide range of hole doping. We observe that $p_c \propto \hbar/\xi$ scales with $T_c$ and therefore superfluid density $n_s(T\rightarrow0)$ in our two-dimensional cuprate films. This relationship was famously predicted by a universal model of the cuprates with a \textit{doping-independent} superconducting gap, but has not been observed by high field measurements of the coherence length $\xi$ due to field-induced phenomena not included in the theory.