The role of the coherence length for the establishment of global phase coherence in three-dimensional arrays of ultra-thin quasi-one-dimensional superconducting Pb and NbN nanowires

TL;DR

This study investigates how the coherence length influences the development of global phase coherence in 3D arrays of ultra-thin superconducting nanowires, revealing material-dependent differences in superconducting transition behavior.

Contribution

It demonstrates that the small coherence length in NbN nanowires suppresses Josephson coupling, preventing the 1D to 3D superconducting transition seen in Pb nanowires.

Findings

Pb nanowire arrays show a crossover to 3D superconductivity with zero resistance.

NbN nanowire arrays lack this crossover due to suppressed Josephson coupling.

Material coherence length critically affects phase coherence in nanowire arrays.

Abstract

We have fabricated 5 nm ultra-thin NbN nanowires that form a dense and regular array in the linear channels of mesoporous SBA-15 silica substrates. Bulk NbN is a well-known classical superconductor with Tc of 16 K. We show that, by being incorporated into this nanostructure, the composite material exhibits typical quasi-one-dimensional characteristics. We compare the superconducting properties with those of superconducting Pb nanowires of same dimensionality in identical configuration within the linear SBA-15 pores. While Pb nanowire arrays show a pronounced crossover from 1D superconductivity at high temperatures to a 3D bulk superconducting state in the low temperature regime with true zero resistance triggered by transversal Josephson interaction, this transition appears to be completely absent in the NbN nanowire array. The small coherence length in NbN, which strongly suppresses the Josephson coupling is discussed as the origin of this difference.