The in-plane paraconductivity in La_{2-x}Sr_xCuO_4 thin film superconductors at high reduced-temperatures: Independence of the normal-state pseudogap

TL;DR

This study measures in-plane paraconductivity in La_{2-x}Sr_xCuO_4 thin films across various doping levels, finding that superconducting fluctuations are largely unaffected by the normal-state pseudogap even at high reduced temperatures.

Contribution

It demonstrates that the in-plane paraconductivity above Tc is independent of the pseudogap in underdoped LSxCO films, extending the Gaussian-Ginzburg-Landau analysis to high reduced temperatures.

Findings

Paraconductivity is doping-independent above Tc.

Superconducting fluctuations are unaffected by the pseudogap.

Gaussian-Ginzburg-Landau approach with cutoff describes data well.

Abstract

The in-plane resistivity has been measured in $La_{2-x}Sr_xCuO_4$ (LSxCO) superconducting thin films of underdoped ($x=0.10,0.12$), optimally-doped ($x=0.15$) and overdoped ($x=0.20,0.25$) compositions. These films were grown on (100)SrTiO$_3$ substrates, and have about 150 nm thickness. The in-plane conductivity induced by superconducting fluctuations above the superconducting transition (the so-called in-plane paraconductivity, $\Delta\sigma_{ab}$) was extracted from these data in the reduced-temperature range $10^{-2}\lsim\epsilon\equiv\ln(T/\Tc)\lsim1$. Such a $\Delta\sigma_{ab}(\epsilon)$ was then analyzed in terms of the mean-field--like Gaussian-Ginzburg-Landau (GGL) approach extended to the high-$\epsilon$ region by means of the introduction of a total-energy cutoff, which takes into account both the kinetic energy and the quantum localization energy of each fluctuating mode. Our results strongly suggest that at all temperatures above Tc, including the high reduced-temperature region, the doping mainly affects in LSxCO thin films the normal-state properties and that its influence on the superconducting fluctuations is relatively moderate: Even in the high-$\epsilon$ region, the in-plane paraconductivity is found to be independent of the opening of a pseudogap in the normal state of the underdoped films.