Self-Aligned Nanoscale SQUID on a Tip

Abstract

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 μm² displays flux sensitivity of 1.8 × 10⁻⁶ Φ₀/Hz^1/2 and operates in fields as high as 0.6 T. With projected spin sensitivity of 65 μ_B/Hz^1/2 and high bandwidth, the SQUID on a tip is a highly promising probe for nanoscale magnetic imaging and spectroscopy.