Detection of the Meissner effect with a diamond magnetometer

We examine the possibility of probing superconductivity effects in metal nanoclusters via diamond magnetometry. Metal nanoclusters have been proposed as constitutive elements of high-Tc superconducting nanostructured materials. Magnetometry based on the detection of spin-selective fluorescence of nitrogen-vacancy (NV) centers in diamond is capable of nanoscale spatial resolution and can be used as a tool for investigating the properties of single or multiple clusters interacting among each other or with a surface. We have carried out sensitivity estimates and experiments to understand how these magnetometers could be used in such a situation. We detected the flux exclusion effect in a superconductor by monitoring the magnetic resonance spectrum of a large ensemble of NV centers in diamond. Our results show that phase transitions can be ascertained in a bulk superconductor with this technique. We also discovered temperature-dependent behavior of the zero-field splitting parameter D and conclude that the general implementation of such measurements may require compensation schemes.