Self-aligned nanoscale SQUID on a tip

A nanometer-sized superconducting quantum interference device (nanoSQUID) is fabricated on the apex of a sharp quartz tip and integrated into a scanning SQUID microscope. A simple self-aligned fabrication method results in nanoSQUIDs with diameters down to 100 nm with no lithographic processing. An aluminum nanoSQUID with an effective area of 0.034 $\mu$m${}^2$ displays flux sensitivity of 1.8$\cdot {10}^{-6}$ $\Phi_0/$\mathrm{H}\mathrm{z}$^{1/2} and operates in fields as high as 0.6 T. With projected spin sensitivity of 65 ${\mu }_B\mathrm{/}{\mathrm{H}\mathrm{z}}^{1\mathrm{/}2}$ and high bandwidth, the SQUID on a tip is a highly promising probe for nanoscale magnetic imaging and spectroscopy.