Low Field Magnetic Response of the Granular Superconductor LaSrCuO

TL;DR

This study investigates the low-field magnetic response of granular LaSrCuO, revealing irreversible intergrain Josephson currents and a glassy state formation, influenced by its d-wave superconductivity, with a new fractal model proposed for irreversibility.

Contribution

It introduces a novel fractal model to describe irreversibility in the magnetic response of granular high-temperature superconductors like LaSrCuO.

Findings

Intergrain Josephson currents are fully irreversible and produce shielding response.

The system of Josephson currents freezes into a glassy state without external magnetic field.

A new fractal model explains the irreversibility observed in the magnetic response.

Abstract

The properties of the low excitation field magnetic response of the granular high temperature (HTSC) superconductor LaSrCuO have been analyzed at low temperatures. The response of the Josephson currents has been extracted from the data. It is shown that intergrain current response is fully irreversible, producing shielding response, but do not carry Meissner magnetization. Analysis of the data shows that the system of Josephson currents freezes into a glassy state even in the absense of external magnetic field, which is argued to be a consequence of the d-wave nature of superconductivity in LaSrCuO. The macroscopic diamagnetic response to very weak variations of the magnetic field is shown to be strongly irreversible but still qualitatively different from any previously known kind of the critical-state behaviour in superconductors. A phenomenological description of these data is given in terms of a newly proposed ``fractal'' model of irreversibility in superconductors.