Hole Doping Dependence of the Coherence Length in $La_{2-x}Sr_xCuO_4$ Thin Films

TL;DR

This study measures how the coherence length in La_{2-x}Sr_xCuO_4 thin films varies with doping, revealing a decrease in underdoped and an increase in overdoped regions, challenging some existing models of pseudogap behavior.

Contribution

First direct derivation of doping dependence of coherence length in La_{2-x}Sr_xCuO_4 thin films from low temperature data.

Findings

Coherence length decreases in underdoped region.

Coherence length increases in overdoped region.

Results challenge the pre-formed pairing model regarding pseudogap and upper-critical field.

Abstract

By measuring the field and temperature dependence of magnetization on systematically doped $La_{2-x}Sr_xCuO_4$ thin films, the critical current density $j_c(0)$ and the collective pinning energy $U_p(0)$ are determined in single vortex creep regime. Together with the published data of superfluid density, condensation energy and anisotropy, for the first time we derive the doping dependence of the coherence length or vortex core size in wide doping regime directly from the low temperature data. It is found that the coherence length drops in the underdoped region and increases in the overdoped side with the increase of hole concentration. The result in underdoped region clearly deviates from what expected by the pre-formed pairing model if one simply associates the pseudogap with the upper-critical field.