ABSOLUTE MAGNETIC PENETRATION DEPTH OF THIN-FILM NIOBIUM MEASURED BY FLUXOID QUANTIZATION

The absolute magnetic penetration depth of a superconducting niobium f ilm is measured using fluxoid quantization. Laser pulses drive part.of a thin, planar niobium loop normal, changing its quantum fluxoid stat e. We determine the total inductance of the loop by measuring the coup ling of the fluxoid to a superconducting quantum interference device a t various loop temperatures. We fit the temperature dependence of the inductance data to the Bardeen-Cooper-Schrieffer (BCS) theory to deter mine the magnetic and kinetic inductances. The kinetic inductance is d irectly related to the penetration depth through the geometry of the l oop, and the measured penetration depth agrees well with the BCS theor y.