Scanning nanoSQUID-on-tip microscopy with single spin sensitivity

A scanning probe microscope based on a unique nanoSQUID which is fabricated on the apex of a quartz tip has been developed. The nanoSQUID-on-tip device is fabricated by pulling a quartz tube into a sharp pipette with diameters down to 50 nm followed by deposition of a thin superconducting film onto the sides and the apex of the pipette. The devices operate at 4 K in applied magnetic fields of up to 1T and display an extremely low flux noise. As a result a record spin sensitivity of better than 1 μ_B/Hz^1/2 is achieved that is sufficient for detecting the magnetic moment of a single electron. Using a quartz tuning-fork based AFM technique the nanoSQUID can be scanned few nm above the surface of the sample. The combination of high sensitivity, high spatial resolution, wide bandwidth, and close proximity to the sample opens the pathway to direct investigation and imaging of static and dynamic magnetic phenomena on the nanoscale. Preliminary results of study of vortex dynamics in superconductors and magnetic structures in doped topological insulator will be presented.