Vortex lattice instability at the nanoscale in a parallel magnetic field

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Vortex lattice instability in superconductors occurs at high vortex velocities, leading to a sudden transition to the normal state.
• Understanding nanoscale effects is crucial for advanced superconducting device applications.

Purpose of the Study:

• To experimentally investigate the influence of nanoscale geometry on vortex lattice instability in ultra-thin superconducting films.
• To examine the effect of magnetic field orientation on vortex lattice instability.
• To compare critical currents and instability currents in different configurations.

Main Methods:

• Fabrication of submicron bridges from ultra-thin films (few nanometers) of Niobium Nitride (NbN) and Niobium Titanium Nitride (NbTiN).
• Experimental measurements of critical currents (Ic) and instability currents (I*) under magnetic fields applied parallel and perpendicular to the c-axis.
• Analysis of the magnetic field dependence of current switching behavior.

Main Results:

• Vortex lattice instability was observed in both NbN and NbTiN ultra-thin films, irrespective of the magnetic field orientation.
• An unusual 'flying birds' feature was identified in the parallel magnetic field configuration, where the ratio I*/Ic approached 1.
• The ultra-thin film geometry with in-plane magnetic fields mimics nanoscale bridge narrowing.

Conclusions:

• The study demonstrates that nanoscale effects significantly influence vortex lattice instability in superconductors.
• The 'flying birds' feature in the parallel field configuration offers potential for practical applications in superconducting nanostructures.
• Scaling down film thickness and orienting the magnetic field in-plane are key strategies for controlling vortex dynamics in nanodevices.