Negative magnetoresistance in the nearest-neighbour hopping conduction in granular gold film

TL;DR

This study investigates the negative magnetoresistance observed in granular gold films near the percolation threshold, revealing unusual behavior in the hopping conduction regime at low temperatures.

Contribution

It provides the first detailed analysis of negative magnetoresistance in nearest-neighbour hopping conduction in granular gold films near the percolation threshold.

Findings

Negative magnetoresistance described by elta R(H)/R(0)   -H^2/T

Resistance exhibits exponential dependence on temperature and voltage at low temperatures

Behavior is observed in films near the percolation threshold at low temperatures

Abstract

The low temperature (0.5-55 K) conduction of semicontinuous gold film vacuum deposited at T \approx 50 K is studied. The film is near the percolation threshold (thickness 3.25 nm). Its resistance is extremely sensitive to the applied voltage U. At low enough U the film behaves as an insulator (two-dimensional granular metal). In this state the dependences R(T) \propto \exp (1/T) (for T \leq 20 K) and R(U) \propto \exp (1/U)) (for T \leq 1 K and U > 0.1 V) are observed. Magnetoresistance (MR) is negative and can be described by \Delta R(H)/R(0) \propto -H^2/T. This negative MR which manifests itself for nearest-neighbour hopping is rather uncommon and, up to now, has not been clarified. The possible mechanisms of such case of negative MR are discussed.