Observation of enhanced fluctuation diamagnetism in lanthanum superconductors with dilute magnetic impurities

TL;DR

This study measures fluctuation diamagnetism in lanthanum superconductors with magnetic and nonmagnetic impurities, revealing an unexpected enhancement in magnetic impurity-doped samples due to interactions with fluctuating Cooper pairs.

Contribution

It demonstrates an anomalous increase in fluctuation diamagnetism in lanthanum with dilute magnetic impurities, indicating a new interaction mechanism not predicted by existing theories.

Findings

Fluctuation diamagnetism matches theory in pure La and La-Lu alloys.

La-Pr alloys show about five times larger FD than expected.

Enhanced FD suggests interaction between Cooper pairs and magnetic impurities.

Abstract

The fluctuation-induced diamagnetism (FD), associated with the presence of precursor Cooper pairs in the normal state, has been measured in lanthanum with dilute magnetic (Pr) and nonmagnetic (Lu) impurities. It is found that while for pure La and La-Lu alloys the FD agrees, as expected, with the theoretical predictions, it is much larger for La-Pr alloys (around a factor 5 for La-2at.%Pr). These results suggest the existence of an indirect contribution to the FD arising from the interaction between fluctuating Cooper pairs and magnetic impurities.