EPR study of superconductors

TL;DR

This paper reviews the history of electron paramagnetic resonance studies in superconductors from 1970 to 1990, highlighting key experimental discoveries including impurity resonance, magnetic interactions, impurity ordering, and evidence of heterogeneity in high-$T_c$ superconductors.

Contribution

It presents the first observation of EPR of impurities in a type II superconductor and provides new insights into magnetic interactions and heterogeneity in high-$T_c$ materials.

Findings

First EPR observation of impurities in a type II superconductor

Indication of long-range exchange interactions due to superconducting correlations

Evidence of impurity magnetic ordering and heterogeneity in high-$T_c$ superconductors

Abstract

Historical review on the studies of the electron paramagnetic resonance in superconductors performed in the period from 1970 to 1990 at the Kazan Physical Technical Institute of the Russian Academy of Sciences (group of Dr. E. G. Kharakhash'yan) in collaboration with Kazan State University (group of Prof. B. I. Kochelaev) and with the Institute for Physical Problems of Russian Academy of Sciences (group of Prof. N. E. Alekseevskii) is presented. We have observed for first time electron paramagnetic resonance of impurities in a type II superconductor; found indication for a long-range exchange interaction between magnetic impurities arising due to the superconducting correlations; observed the magnetic ordering of impurities in the superconducting state; and, finally, we found one of the first evidences for heterogeneity of the 1:2:3 high-$T_c$ superconductor which is its natural property