Magnetoresistance of Granular Superconducting Metals in a Strong Magnetic Field

TL;DR

This paper investigates how superconducting fluctuations affect the magnetoresistance of granular superconductors in strong magnetic fields, showing that fluctuations cause negative magnetoresistance by reducing the density of states without aiding conduction.

Contribution

It provides a theoretical analysis of superconducting fluctuation effects on magnetoresistance in granular superconductors under strong magnetic fields, highlighting the role of density of states reduction.

Findings

Superconducting fluctuations reduce the one-particle density of states at low temperatures.

Resistivity exceeds classical values in the normal state due to fluctuations.

Negative magnetoresistance arises as magnetic field suppresses superconducting effects.

Abstract

The magnetoresistance of a granular superconductor in a strong magnetic field is considered. It is assumed that this field destroys the superconducting gap in each grain, such that all interesting effects considered in the paper are due to superconducting fluctuations. The conductance of the system is assumed to be large, which allows us to neglect all localization effects as well as the Coulomb interaction. It is shown that at low temperatures the superconducting fluctuations reduce the one-particle density of states but do not contribute to transport. As a result, the resistivity of the normal state exceeds the classical resistivity approaching the latter only in the limit of extremely strong magnetic fields, and this leads to a negative magnetoresistance. We present detailed calculations of physical quatities relevant for describing the effect and make a comparison with existing experiments.