Accuracy and sensitivity of penetration depth measurements in superconducting films using the mutual inductance method

摘要

The London penetration depth of a superconducting film may be determined using a measurement of the mutual inductance between a pair of small coils along a common axis, located on opposite sides of the film. Two coil configurations are compared: a simple "dipole" winding (all turns of the same polarity), and a "quadrupole" coil with counter wound dipoles mounted one above the other. It is shown that generally the simple dipole arrangement gives superior results. For a typical YBCO film the demonstrated resolution in penetration depth is <0.01 nm. Uncertainties in coil dimensions can produce a systematic error in the absolute magnitude of the penetration depth ～5%, Random errors are less than 5% for substrates as small as 7 mm effective diameter and films as thick as 750 nm.