Widefield NV Magnetic Field Reconstruction for Probing the Meissner Effect and Critical Current Density under Pressure

TL;DR

This paper demonstrates a novel widefield NV magnetometry technique to quantitatively reconstruct magnetic fields in a superconductor under high pressure, revealing the Meissner effect and critical current density with high spatial resolution.

Contribution

It introduces a method for quantitative magnetic field reconstruction using NV centers under pressure, enabling detailed superconductivity studies at high pressures.

Findings

Reconstructed the magnetic field distribution around a superconductor under pressure.

Measured the Meissner effect and extracted the critical current density.

First application of widefield NV magnetometry for high-pressure superconductivity analysis.

Abstract

The spatial distribution of a magnetic field can be determined with micrometer resolution using widefield nitrogen vacancy (NV) center magnetic imaging. Nevertheless, reconstructing the magnetic field from the raw data can be challenging due to the degeneracy of the four possible NV axes and the tremendous amount of data. While a qualitative approach is sufficient for most analyses, a quantitative analysis offers deeper insight into the physical system. Here, we apply NV widefield magnetic imaging to a HgBa$_{2}$Ca$_{2}$Cu$_{3}$O$_{8+\delta}$ (Hg-1223) superconducting microcrystal at a pressure of 4 GPa. We fit the results with solutions from the Hamiltonian describing the NV center ground state and take into account the relative intensities of the resonances to determine the local magnetic field magnitude and angle. Thus, we reconstruct the temperature-dependent expulsion of the magnetic field due to the Meissner effect around the superconductor. By comparing the resulting parameters to Brandt's model, which describes the magnetic behavior of a type-II superconductor, we extract the critical current density $j_c$. Overall, this work showcases the first widefield quantitative reconstruction of the Meissner effect under pressure and an optical method to study critical current density. Thus, it provides new insights into the application of NV magnetometry to superconductivity research at high pressures.