Work during the first half of the project has focused on setting up a scanning magnetometer operating at sub-Kelvin temperatures. This build-up has resulted in a one-of-its-kind instrument that, to the best of our knowledge, is the only scanning diamond magnetometer system world-wide operating at such low temperatures. The successful operation was demonstrated by imaging the Meissner screening from superconducting aluminum micro-discs. These experiments also verified that NV centers remain stable at those temperatures and retain their high sensitivity.
In a second part, several key demonstrations were made by imaging several prominent samples. The first demonstration included the imaging of current flow in bilayer and monolayer graphene devices; in the latter, the formation of current whirlpools could be observed, which are a hallmark of hydrodynamic transport. Notably, this observation could already be made at room temperature, which is rare for these kinds of transport experiments. A second demonstration included the imaging of gate-controlled suppression of superconductivity (a “superconducting transistor”) via the Meissner screening. While many resistance-based experiments have been conducted, our instrument allowed for the first direct observation of this notable effect by imaging.
The instrumentation and capabilities realized with the ERC grant will on the one hand enable many more imaging studies of nanoscale electronic transport and superconductivity. Further, we will use some of the knowledge gained to study magnetotransport in the context of spintronics. On the other hand, we expect that some of the technology developed can be exploited in the future to build more compact, more stable diamond NV sensors, especially for cryogenic experiments.
