Expansion of Vortex Cores by Strong Electronic Correlation in La$_{2-x}$Sr$_x$CuO$_4$ at Low Magnetic Induction

TL;DR

This study uses muon spin rotation to measure vortex core sizes in La$_{2-x}$Sr$_x$CuO$_4$, revealing an unusual increase at low doping levels due to strong electronic correlations, challenging conventional theories.

Contribution

It provides the first experimental evidence of vortex core expansion driven by electronic correlations in cuprate superconductors.

Findings

Vortex core radius increases with decreasing temperature at low doping.

Core size is larger than Ginzburg-Landau coherence length at low doping.

Core size decreases with increasing doping, consistent with a correlation-driven model.

Abstract

The vortex core radius \rv, defined as the peak position of the supercurrent around the vortex, has been determined by muon spin rotation measurements in the mixed state of \lscox for $x=0.13$, 0.15, and 0.19. At lower doping (x=0.13 and 0.15), \rv(T) increases with decreasing temperature T, which is opposite to the behavior predicted by the conventional theory. Moreover, \rv(T\to0) is significantly larger than the Ginsburg-Landau coherence length determined by the upper critical field, and shows a clear tendency to decrease with increasing the doping x. These features can be qualitatively reproduced in a microscopic model involving antiferromagnetic electronic correlations.