MEASUREMENTS OF KINETIC INDUCTANCE OF SUPERCONDUCTING LINEAR STRUCTURES

The kinetic inductance Lk is associated with the inertial mass of the current carriers. For a long superconductor of length l and very small cross-sectional area σ, Lk = (m* / nse* 2) (l/σ) and is the main contribution to the temperature-dependent inductance LT. We have measured LT in superconducting tin wires and thin film meander lines by a technique which uses a counter to determine frequency changes of a 15 MHz tunnel-diode oscillator whose tank circuit contains LT. The measured frequency changes are proportional to z = [λ(t)/λ(0)]BCS for wires and thick films; for thin films the frequency changes are proportional to z2. This result agrees with calculations of LT from the London theory and the values of λ(0) agree well with the values expected for these samples. This technique allows measurement of the carrier concentration or penetration depth in thin films over the whole H, T plane of the superconducting state and can be independent of the penetration law assumed. Frequency shifts observed with thin film alumimum meander lines have been used to detect changes of temperature of 5∼10-7°K, changes of magnetic field of 10-5 G, and changes of current associated with one quantum in a flux quantum magnetometer. © 1969 The American Institute of Physics.