Local characterization of a heavy-fermion superconductor via sub-Kelvin magnetic force microscopy

TL;DR

This study employs sub-Kelvin magnetic force microscopy to locally characterize a heavy-fermion superconductor, measuring key properties like penetration depth, vortex pinning, and inhomogeneities with high spatial resolution.

Contribution

It introduces a novel sub-Kelvin magnetic force microscopy approach for local superconductor characterization, providing detailed insights into vortex behavior and material inhomogeneities.

Findings

Measured London penetration depth as 435 nm

Estimated critical current density as 9×10^4 A/cm²

Resolved local inhomogeneities at micrometer scale

Abstract

Using magnetic force microscopy operating at sub-Kelvin temperatures we characterize the heavy-fermion superconductor CeCoIn$_5$. We pinpoint the absolute London penetration depth $\lambda(0) = 435 \pm 20$ nm and report its temperature dependence, which is closely linked to the symmetry of the superconducting gap. In addition, we directly measure the pinning force of individual Abrikosov vortices and estimate the critical current density $j_c = 9 \times 10^4$ A/cm$^2$. In contrast to the related, well-established tunnel diode oscillator technique, our method is capable of resolving inhomogeneities $locally$ on the micrometer-scale at ultra-low temperature.