Intergranular flux pinning in underdoped and overdoped R(1-x)CaxBa2Cu3Oz (R=Y,Gd; x=0,0.2) samples

TL;DR

This study investigates how intergranular flux pinning varies with doping levels in R(1-x)CaxBa2Cu3Oz superconductors, revealing correlations between doping, vortex dimensionality, and flux pinning energy.

Contribution

It provides new insights into the effects of calcium doping on flux pinning and vortex behavior in high-temperature superconductors.

Findings

Underdoped samples exhibit S-I-S behavior with low activation energy.

Overdoped samples show S-N-S behavior with higher activation energy.

Calcium substitution enhances intergranular activation energy and alters vortex dimensionality.

Abstract

The temperature dependences of AC magnetic susceptibility at different magnetic field amplitudes and frequencies are investigated for underdoped and overdoped R(1-x)Ca(x)Ba(2)Cu(3)O(7-delta)(R=Y; Gd and x=0; 0.2) polycrystalline samples. The activation energy, Ea, for thermally assisted flux flow (TAFF) in intergranular region is determined. It was established that a correlation exists between the intergranular critical current and flux pinning activation energy. In underdoped samples the intergranular current shows S-I-S behaviour and the activation energy is small, while in overdoped samples the intergranular current is changed to S-N-S type and the activation energy increases. 2D pancake vortices are characteristic of underdoped samples, while 3D vortex system exists in overdoped samples. In fact we demonstrate that Ca substitution not only increases carrier concentration, but improves intergranular activation energy for TAFF.