Inductive conductance measurements in two-dimensional superconducting systems

Abstract

A two-coil mutual-inductance technique for measuring the complex ac response of a two-dimensional (2-D) superconductor to a weak ac magnetic field is described. Analytical and numerical methods are presented which allow extraction of the complex ac conductance of the superconductor from the signal voltage induced in the detection coil by the screening currents flowing in the sample. The method is illustrated by measurements of the ac conductance of a square network of aluminum wires from which the penetration depths of both the network and (granular) aluminum are deduced. It is shown that the method provides a powerful tool to observe characteristic features associated with critical phenomena in 2-D superconducting systems.

Dynamical reentrance and geometry imposed quantization effects in Nb–AlOx–Nb Josephson junction arrays

“…When these coils are located near the surface of the film, the response, i.e., the complex output voltage V, does not depend on the radius of the film or its properties near the edges. In the reflection technique (Jeanneret et al 1989) an excitation coil (primary) coaxially surrounds a pair of counter-wound pick up coils (secondaries). When there is no sample in the system, the net output from these secondary coils is close to zero since the pick up coils are close to identical in shape but are wound in opposite directions.…”

“…To measure the complex AC susceptibility in our arrays we used a high-sensitive home-made susceptometer based on the so-called screening method in the reflection configuration (Jeanneret et al 1989, Araujo-Moreira et al 2002, as shown in previous sections. The experimental system was calibrated by using a high-quality niobium thin film.…”

Observation of Ising-like critical fluctuations in frustrated Josephson junction arrays with modulated coupling energies

“…To explore the properties of the array in the critical region, we measured its complex ac sheet conductance G(ω, T ) at f=1/2 using a SQUIDoperated two-coil mutual inductance technique [9], which allows to probe critical fluctuations over a frequency range covering more than 5 decades (0.1 Hz -10 kHz). At the temperatures of interest (T ∼ = 5K) we estimate that the vortex diffusion…”

Geometrical Effects in Two-Dimensional Arrays of Josephson Junctions

“…M(x) is the mutual-inductance distribution resulting from the geometry of the measuring system. See Jeanneret et al (1989) for specific details on the derivation of this equation. 18 We tested this by using a square-wave signal as our input signal.…”

“…To conduct contactless ac measurements, we use a two-coil mutual-inductance technique similar to that outlined by Jeanneret et al (1989). Our main measurement apparatus consists of a drive coil of radius Rd--0.42 cm and a pair of astatically wound receive coils of radius Rr=0.24 cm which is coaxially mounted within the drive coil (see Fig.…”