Emergence of superconductivity in the cuprates via a universal percolation process

TL;DR

This study reveals that superconductivity in cuprates emerges through a universal percolation process driven by inhomogeneity, as evidenced by nonlinear conductivity measurements that show exponential decay above T_c.

Contribution

It demonstrates that the emergence of superconductivity in cuprates can be explained by a simple percolation model, challenging traditional Ginzburg-Landau theory explanations.

Findings

Nonlinear conductivity vanishes exponentially above T_c

Universal temperature-scaling characterized by T_0

Percolation model successfully explains superconductivity emergence

Abstract

A pivotal step toward understanding unconventional superconductors would be to decipher how superconductivity emerges from the unusual normal state upon cooling. In the cuprates, traces of superconducting pairing appear above the macroscopic transition temperature $T_c$, yet extensive investigation has led to disparate conclusions. The main difficulty has been the separation of superconducting contributions from complex normal state behaviour. Here we avoid this problem by measuring the nonlinear conductivity, an observable that is zero in the normal state. We uncover for several representative cuprates that the nonlinear conductivity vanishes exponentially above $T_c$, both with temperature and magnetic field, and exhibits temperature-scaling characterized by a nearly universal scale $T_0$. Attempts to model the response with the frequently evoked Ginzburg-Landau theory are unsuccessful. Instead, our findings are captured by a simple percolation model that can also explain other properties of the cuprates. We thus resolve a long-standing conundrum by showing that the emergence of superconductivity in the cuprates is dominated by their inherent inhomogeneity.