Complex Phase-Fluctuation Effects Correlated with Granularity in Superconducting NbN Nanofilms

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Superconducting nanofilms exhibit dimensional crossovers, leading to phenomena like the Berezinskii-Kosterlitz-Thouless (BKT) transition.
• Further reduction in dimensionality to quasi-1D systems with disorder can induce quantum and thermal phase slips (PS).
• Both BKT transitions and PS are complex, experimentally challenging phase fluctuation phenomena.

Purpose of the Study:

• To characterize superconducting niobium nitride (NbN) nanofilms with thicknesses below 15 nm.
• To investigate the emergence and interplay of BKT transitions and PS events in these nanostructures.
• To understand the tunability of these phenomena with temperature and film thickness.

Main Methods:

• Fabrication of superconducting NbN nanofilms on various substrates.
• Temperature-dependent resistivity measurements.
• Current-voltage (I-V) characteristic analysis.

Main Results:

• Observed clear experimental evidence for both BKT transitions and PS events in NbN nanofilms.
• Demonstrated contemporary occurrence and tunable evolution of BKT and PS with temperature and thickness.
• Traced the continuous evolution from quantum to thermal PS in a specific sample.
• Attributed these phenomena to nano-conducting paths in a granular NbN system.

Conclusions:

• The interplay between nano-conductive path size and superconducting coherence length governs the observed complex phase phenomena.
• NbN nanofilms serve as a tunable system for studying the transition from 3D to 2D superconductivity and phase slip events.
• This work provides a pathway to experimentally probe and control quantum and thermal phase fluctuations in superconducting nanostructures.