Superconductivity in im-miscible Cu-Nb phase separated nano-composite thin films

TL;DR

This study investigates how phase separation and grain size in Nb-Cu nanocomposite films influence their superconducting properties, revealing that increased Cu content leads to reduced Tc, Hc2, and Ic, with phase fluctuations affecting superconductivity.

Contribution

The paper provides new insights into the effects of phase separation and composition on superconductivity in Nb-Cu nanocomposites, highlighting the role of phase fluctuations.

Findings

Superconducting transition temperature decreases with more Cu.

Critical magnetic field and current decrease with Cu content.

Presence of phase fluctuations impacts superconducting coherence.

Abstract

Superconductivity in granular films is controlled by the grain size and the inter-grain coupling. In a two-component granular system formed by a random mixture of a normal metal (N) and a superconductor (S), the superconducting nano-grains may become coupled through S-N weak links, thereby affecting the superconducting properties of the network. We report on the study of superconductivity in immiscible Nb-Cu nanocomposite films with varying compositions. The microstructure of the films revealed the presence of phase separated, closely spaced, nano-grains of Nb and Cu whose sizes changed marginally with composition. The superconducting transition temperature (Tc0) of the films decreased with increasing concentration of Cu with a concomitant decrease in the upper critical field (Hc2) and the critical current (Ic). Our results indicate the presence of superconducting phase fluctuations in all films with varying Nb:Cu content which not only affected the temperature for the formation of a true phase coherent superconducting condensate in the films but also other superconducting properties.