arXiv subjects

A. Frydman

Publications and source records attributed to A. Frydman.

22 records · Page 2Linked to original sources

arXiv2002

Universal transport in 2D granular superconductors

The transport properties of quench condensed granular superconductors are presented and analyzed. These systems exhibit transitions from insulating to superconducting behavior as a function of inter-grain spacing. Superconductivity is characterized by broad transitions in which the resistance drops exponentially with reducing temperature. The slope of the log R versus T curves turns out to be universaly dependent on the normal state film resistance for all measured granular systems. It does not depend on the material, critical temperature, geometry, or experimental set-up. We discuss possible physical scenarios to explain these findings.

cond-mat.supr-con↗

arXiv2001

The superconductor insulator transition in systems of ultrasmall grains

We present transport measurements on quench condensed granular Pb films in which the grains are 40-80Åin diameter. These films show a cross over from an insulator to a superconductor behavior as the nominal thickness of the layer is increased. This transition is different in nature than those seen in quench condensed systems reported in the past where the films were either uniform or granular with grain sizes on the order of 200Å. We discuss possible physical mechanisms for these transitions.

cond-mat.mes-hall↗

arXiv1998

Excess conductance in normal-metal/superconductor junctions

The current-voltage characteristics of Au/InOx/Pb tunnel junctions exhibit peculiar zero-bias anomalies. At low temperature the zero-bias resistance attains values that are smaller than the normal state resistance by a factor that often esceeds 2. The width of this anomaly increases with the thickness of the InOx layer. The possibility that these features arise from the nature of the barrier being an Anderson insulator is discussed.

cond-mat↗

arXiv1998

Magnetoresistance of Granular Ferromagnets - Observation of a Magnetic Proximity Effect?

We have observed a superparamagnetic to ferromagnetic transition in films of isolated Ni grains covered by non-magnetic overlayers. The magnetoresistance (MR) of the films was measured as a function of the overlayer thickness. Initially, the granular Ni films exhibited negative MR curves peaked at H=0. As different materials were deposited onto the grains hysteresis developed in the MR. This behavior is ascribed to an increase of the typical domain size due to magnetic coupling between grains. The strength of the inter-grain coupling is found to correlate with the magnetic susceptibility of the overlayer material. We discuss possible mechanisms for this coupling and suggest that the data may reflect the existence of a magnetic proximity effect (analogous to the well-known effect in superconductivity) in which a ferromagnetic moment is induced in the metallic non-magnetic medium.

cond-mat.mes-hall↗