Measuring the Lower Critical Field of Superconductors Using Nitrogen-Vacancy Centers in Diamond Optical Magnetometry

In condensed matter physics, knowing the lower critical magnetic field Hc1 is necessary to evaluate the superfluid density, which can provide insight into the gap structure gap and mechanism of superconductivity in a type-II superconductor. Measuring Hc1 is complicated by the distortion of a magnetic field around the sample, and by the sensitivity and spatial resolution of the chosen technique. This work demonstrates minimally invasive vector magnetometry based on optically detected magnetic resonance of N-V centers in diamond, which, with the help of revised demagnetization corrections for real-world nonellipsoidal samples, provides a sensitive method to measure Hc1.