Imaging the Meissner Effect and Flux Trapping of Superconductors under High Pressure using N-V Centers

TL;DR

This paper demonstrates the use of nitrogen-vacancy (N-V) center magnetometry to image the Meissner effect and flux trapping in superconductors under high pressure, achieving micrometer resolution and revealing local superconducting properties.

Contribution

The study introduces a high-resolution N-V magnetometry technique for mapping superconductivity and flux trapping in materials under high pressure, expanding microscopic analysis capabilities.

Findings

Successfully mapped magnetic field expulsion in a high-pressure superconductor

Detected heterogeneities and local critical temperatures within the sample

Identified flux pinning zones through flux trapping maps

Abstract

Pressure is a key parameter for tuning or revealing superconductivity in materials and compounds. Many measurements of superconducting phase transition temperatures have been conducted using diamond anvil cells (DACs), which provide a wide pressure range and enable concomitant microscopic structural characterization of the sample. However, the inherently small sample volumes in DACs complicate the unambiguous detection of the Meissner effect, the hallmark of superconductivity. Recently, the Meissner effect in superconductors within a DAC was successfully demonstrated using diamond nitrogen-vacancy (N-V) widefield magnetometry, a non-invasive optical technique. In this work, we show that N-V magnetometry can also map superconductivity with micrometer resolution. We apply this technique to a microcrystal of HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ (Hg-1223) mercury-based cuprate superconductor under 4 GPa of pressure. The method is capable to detect the magnetic field expulsion and heterogeneities in the sample, visible in a set of characteristic parameters as the local critical temperature $T_{c}$. Flux pinning zones are identified through flux trapping maps. This approach could enable detailed investigations of superconductivity of a broad range of materials under high-pressure conditions.