Effects of SQUID Alignment on Penetration Depth Measurements

Scanning SQUID (Superconducting QUantum Interference Device) susceptometry is a powerful tool for measuring a sample’s response to a small, local magnetic field. For example, measuring the diamagnetic susceptibility due to a superconductor as a function of height yields information about the local penetration depth. In our susceptometer geometry, this is accomplished by passing an alternating current through a field coil, then phase sensitively measuring the resulting flux through a smaller concentric pickup loop. The result is then reported in units of flux per ampere of current applied, which is an inductance. Normalizing this figure by the unloaded mutual inductance between the field coil and pickup loop results in a dimensionless susceptibility that depends sensitively on the sample as well as the measurement geometry. In this talk, we discuss the systematic errors introduced by geometric factors such as the sensor height, pitch, and roll in extracting the penetration depth from scanning SQUID susceptometry data, providing insight into the interpretation of future measurements.