Probing Vortex Dynamics in 2D Superconductors with Scanning Quantum Microscope

TL;DR

This paper employs scanning quantum microscopy to visualize and analyze vortex behavior in 2D superconductors, revealing unique vortex arrangements, dynamics, and fluctuations at the nanoscale, advancing understanding of 2D superconductivity.

Contribution

It introduces a high-resolution quantum microscopy technique to study vortex dynamics and fluctuations in 2D superconductors, uncovering phenomena difficult to detect with traditional methods.

Findings

Vortices form a distorted vortex glass rather than a hexagonal lattice.

Vortex size expands and exhibits strong local dynamics due to thermal effects.

Vortex glass melts near the critical temperature, with configurations influenced by cooling conditions.

Abstract

The visualization of the magnetic responses of a two-dimensional (2D) superconducting material on the nanoscale is a powerful approach to unravel the underlying supercurrent behavior and to investigate critical phenomena in reduced dimensions. In this study, scanning quantum microscopy is utilized to explore the local magnetic response of the 2D superconductor 2H-NbSe2. Our technique enables both static and dynamic sensing of superconducting vortices with high sensitivity and a spatial resolution down to 30 nm, unveiling unexpected phenomena linked to the intrinsic 2D nature of the superconductor, which are challenging to detect with more conventional local probes. Vortices do not arrange in a hexagonal lattice, but form a distorted vortex glass with expanding vortex size. A vortex can exhibit strong local dynamics due to thermal excitation. As the critical temperature is approached, a clear melting of the vortex glass is identified, leading to distinct configurations under different cooling conditions. Vortex fluctuations can also be probed through spin Hahn-echo measurements, which reveal the spin decoherence even well below the critical temperature -- and, intriguingly, enhanced decoherence at lower temperatures. Spatiotemporal microscopy of the magnetic dynamics associated with vortex excitations and fluctuations provides direct evidence of 2D superconducting phenomena at the nanoscale.