High-transition temperature superconducting quantum interference device microscope

Abstract

A microscope has been constructed in which a high-transition temperature dc superconducting quantum interference device (SQUID) in vacuum is brought to within 140 μm of samples at room temperature and pressure. The SQUID is mounted on the upper end of a sapphire rod, cooled to liquid nitrogen temperature, below a 75-μm thick sapphire window. Samples can either be placed directly on the window or scanned over the SQUID to produce magnetic images. A square-washer SQUID with inner and outer dimensions of 30 and 50 μm can resolve 130 μm magnetic features. The instrument is intended primarily for biological applications.