Tunable φ Josephson junction ratchet.

We demonstrate experimentally the operation of a deterministic Josephson ratchet with tunable asymmetry. The ratchet is based on a φ Josephson junction with a ferromagnetic barrier operating in the underdamped regime. The system is probed also under the action of an additional dc current, which acts as a counterforce trying to stop the ratchet. Under these conditions the ratchet works against the counterforce, thus producing a nonzero output power. Finally, we estimate the efficiency of the φ Josephson junction ratchet.

Model I-V curves and figures of merit of underdamped deterministic Josephson ratchets.

We propose simple models for the current-voltage characteristics of typical Josephson ratchets. We consider the case of a ratchet working against a constant applied counter force and derive analytical expressions for the key characteristics of such a ratchet: rectification curve, stopping force, input and output powers, and rectification efficiency. Optimization of the ratchet performance is discussed.

Characterization of anomalous pair currents in Josephson junction networks.

Measurements performed on superconductive networks shaped in the form of planar graphs display anomalously large currents when specific branches are biased. The temperature dependences of these currents evidence that their origin is due to Cooper pair hopping through the Josephson junctions connecting the superconductive islands of the array. The experimental data are discussed in terms of theoretical models which predict, for the system under consideration, an inhomogeneous Cooper pair distribution on the superconductive islands of the network as a consequence of a Bose-Einstein condensation phenomenon.

Proton NMR characteristics of a biological system useful for developing in vivo spectroscopy and imaging techniques for tumors.

A model system for in vivo proton NMR studies consisting of a transplantable tumor growing on a rat's tail was investigated at 90 MHz using a high-resolution Fourier transform spectrometer. Spectra were obtained, relaxation times were measured, and the spatial distributions of proton signal intensities were estimated. We conclude that the model could be used for developing both spectroscopy and imaging approaches.