Using NV-centers in diamond for optical magnetic sensing in superconductors*

Magnetic field--dependent fluorescence of nitrogen vacancy (NV) centers in diamond has recently emerged as a promising technology for nanoscale sensing including non-invasive sensitive magnetometry and mapping of the magnetic field distribution. In particular, NV-sensing can be used to study magnetic phenomena in superconductors. After detailed introduction of this novel magneto-sensing technique, we will present results of magnetic measurements on several superconductors, including Ba$_{\mathrm{1-x}}$K$_{\mathrm{x}}$Fe$_{\mathrm{2}}$As$_{\mathrm{2}}$ and type-I materials. Details of the superconducting phase transition, the Meissner state, magnetic flux distribution upon field penetration, exit and trapping will be discussed.