SQUID nature of microwave absorption in a high-Tc superconducting Ho-Ba-Cu-0 single crystal

TL;DR

This study investigates microwave absorption in a high-Tc superconducting Ho-Ba-Cu-O crystal, revealing SQUID-like behavior with a critical current that decreases linearly with temperature, using multiple measurement techniques.

Contribution

It provides evidence for SQUID-like structures in a high-Tc superconductor through detailed microwave absorption analysis and multiple independent measurement methods.

Findings

Absorption spectrum shows SQUID-like behavior with critical current decay.

Hysteresis parameter Li_c/Φ_0 determined consistently by three techniques.

Critical current at 79 K is approximately 3.1×10^{-3} Φ_0.

Abstract

A high-Tc, superconducting Ho-Ba-Cu-O single crystal with Tc=86.8 K is investigated on a modified ESR spectrometer at temperatures T>78 K. A signal is observed, whose spectrum in the range of magnetic fields H<0.7 Oe has the form of equivalent absorption lines with an interval \Delta = 0.009 Oe. Detailed measurements of the dependence of the spectrum on the amplitude of the microwave field, the temperature, and the orientation of the single crystal are reported. It is established that the absorption spectrum exhibits a typical behavior inherent in SQUIDs with a critical current that decays linearly with increasing T. Three different techniques are used to determine the so-called hysteresis parameter of the postulated SQUID: Li_c /\Phi_0 (L and i_c are the inductance and critical current of the SQUID, and \Phi_0 is the quantum of magnetic flux). All three techniques give the same result: Li_c (T=79 K)/\Phi_0= 3.1\pm 0.3, attesting to the existence of a SQUID-like structure in the single crystal.