Superconducting QUantum Interference Devices (SQUIDs) are the world's most sensitive flux detector. They are made of a superconducting loop with two weak links. Our lab has pioneered the design of a gradiometric scanning SQUID. In this case the superconducting loop is shielded except for a small circular area called a pick-up loop. This pick-up loop can be brought close to a sample of interest and scanned above the surface. As the loop is scanned we record the flux that passes through the loop thus creating a magnetic image of the sample. The overall sensitivity of a SQUID magnetometer is determined by it's magnetic flux noise, the pickup loop diameter, and the distance from the sample. We designed a new scanning SQUID with a 200 nm pick-up loop diameter. (Pictured on the left). This new SQUID has a sensitivity of just 70 electron spins per root hertz.
The image shows a scanning electron micrograph of our SQUID's pick-up loop. This loop represents the imaging kernel for our magnetic scanner.
|Nicholas C. Koshnick, Martin E. Huber, Julie A. Bert, Clifford W. Hicks Jeff Large, Hal Edwards, and Kathryn A. Moler, Applied Physics Letters 93 243101 (2008). Full Text|