Magnetic force microscopy versus scanning quantum-vortex microscopy: Probing pinning landscape in granular niobium films

TL;DR

This paper compares magnetic force microscopy and scanning quantum-vortex microscopy for studying vortex pinning in granular niobium films, demonstrating the latter's ability to visualize pinning landscapes with high resolution.

Contribution

It introduces and evaluates scanning quantum-vortex microscopy as a novel technique for probing vortex pinning in superconducting films.

Findings

Quantum-vortex microscopy visualizes grain boundaries at 30 nm resolution.

Vortex trapping occurs near the critical temperature due to weakened pinning.

The method enables detailed exploration of pinning potentials in Nb films.

Abstract

We provide an overview of the methodology and fundamental principles associated with newly developed experimental technique -- scanning quantum-vortex microscopy [Hovhannisyan et al., Commun. Mater., vol. 6, 42 (2025)]. This approach appears promising for experimental studies of vortex pinning phenomena in superconducting films and nanodevices. In particular, we studied the magnetic properties of magnetron-sputtered niobium (Nb) films by low-temperature magnetic force microscopy. As the temperature approaches the superconducting critical temperature, the pinning potential caused by structural defects weakens; consequently, the attractive interaction between the magnetic tip of the cantilever and a single-quantum vortex begins to dominate. In this scenario the magnetic probe is capable of trapping a vortex during the scanning process. Because the dragged vortex continues interacting with structural defects, it serves as an efficient nano-probe to explore pinning potentials and visualize grain boundaries in granular Nb films, achieving resolutions (30 nm) comparable to the superconducting coherence length.