Anomalous precursor diamagnetism at low reduced magnetic fields and the role of Tc inhomogeneities in the superconductors Pb55In45 and underdoped La1.9Sr0.1CuO4

TL;DR

This study investigates anomalous diamagnetism above Tc in superconductors Pb55In45 and La1.9Sr0.1CuO4, showing that Tc inhomogeneities can explain these effects within the Gaussian Ginzburg-Landau framework.

Contribution

It demonstrates that low-field diamagnetic anomalies in both high- and low-Tc superconductors are due to Tc inhomogeneities, aligning with GGL behavior at higher fields.

Findings

Diamagnetic anomalies are explained by Tc inhomogeneities.

Results are consistent with Gaussian Ginzburg-Landau theory.

Tc inhomogeneities are linked to stoichiometric variations.

Abstract

The magnetic field dependence of the magnetization was measured above the superconducting transition in a high-Tc underdoped cuprate La1.9Sr0.1CuO4 and in a low-Tc alloy (Pb55In45). Near the superconducting transition [typically for (T-Tc)/Tc<0.05] and under low applied magnetic field amplitudes [typically for H/Hc2(0)<0.01, where Hc2(0) is the corresponding upper critical field extrapolated to T=0 K] the magnetization of both samples presents a diamagnetic contribution much larger than the one predicted by the Gaussian Ginzburg-Landau (GGL) approach for superconducting fluctuations. These anomalies have been already observed in cuprate compounds by various groups and attributed to intrinsic effects associated with the own nature of these high-Tc superconductors. However, we will see here that our results in both high and low-Tc superconductors may be explained quantitatively, and consistently with the GGL behavior observed at higher fields, by just taking into account the presence in the samples of an uniform distribution of Tc inhomogeneities. These Tc inhomogeneities, which may be in turn associated with stoichiometric inhomogeneities, were estimated from independent measurements of the temperature dependence of the field-cooled magnetic susceptibility under low applied magnetic fields.