Scientists at the Weizmann Institute, Rehovot, Israel, have taken a quantum leap toward understanding the exciting phenomenon of superconductivity. They have created the world’s smallest SQUID, a Superconducting QUantum Interference Device, used to measure magnetic fields, breaking the world record of sensitivity and resolution of such devices.
When certain materials are cooled to extremely low temperatures, they lose all resistance to the flow of electricity and expel the magnetic fields within them. These properties enable their use in MRI scanners for diagnostic imaging of the human body, for trains to “float” in air, and particles to be steered at nearly the speed of light inside particle accelerators.
As opposed to traditional optical microscopy that uses light and lenses to magnify images of small samples, scanning probe microscopy is a technique that uses a probe, in this case, a nano-SQUID, to scan and measure some property at different points of a sample, forming an image of the entire surface like creating a heat map of a hand by taking a thermometer and measuring the temperature at individual points on the hand.
Apart from having very sensitive SQUIDS, there are also geometrical challenges when it comes to using them as scanning probes: they need to be as small as possible to attain the highest image resolution, and they need to get as close as possible to the sample to enable the imaging of ever smaller magnetic features.
The scientists at Weitzmann took a hollow quartz tube and pulled it into a very sharp point then fabricated a SQUID encircling the ring of the tip, which measures a mere 46 nm in diameter, making it the smallest SQUID to date. They proceeded in gluing the tube to a quartz tuning fork and constructing a scanning microscope, which has enabled them to achieve magnetic imaging at distances as small as a few nanometers from the sample.
In contrast, most SQUIDs are made using lithography on flat silicon chips, limiting their size and their ability to get very close to the surface.
This novel instrument is already proving a powerful tool, it is able to measure many other materials other than superconductors.
