Evidence of Current Stabilization after a Long-Time Decay in High-Tc Superconductors

TL;DR

This study observed flux creep in high-Tc superconductors over six months, revealing a transition from decay to stabilization with oscillatory behavior and eventual steady current, challenging classical models.

Contribution

It provides long-term experimental evidence of current stabilization and oscillations in high-Tc superconductors, extending understanding beyond classical flux creep models.

Findings

Low relaxation rates in ferromagnetic field-cooled samples

Oscillatory decay observed around 55 hours

Stable persistent current after 55 days

Abstract

In this work, we studied the flux creep phenomenon over a long period [viz. about 1.5 10E7 s (i.e. for 6 months)] at liquid nitrogen temperature. For this purpose, four high-Tc ring-shaped samples were field-cooled (one sample) or ferromagnetic field-cooled (three samples) in order to induce a persistent current. The resulting current decay was measured using a Hall probe system and the results obtained revealed low relaxation rates in the ferromagnetic field-cooled samples. Also, the experimental data were found to depart from the prediction of the classical models after a long enough time. The slope of the logarithmic current decay plot exhibited an oscillatory phenomenon at ca. 2 10E5 s (about 55 hours). Oscillations vanished at ca. 4-5 10E6 s (46-55 days), after which the induced current remained stable throughout the remainder of the experiencing period.