Strong localization of electrons in quasi-one-dimensional conductors

TL;DR

This paper experimentally investigates electron transport in quasi-one-dimensional GaAs wires, revealing a crossover from weak to strong localization, and uncovers the effects of magnetic field and Coulomb interactions on the density of states.

Contribution

It provides new experimental insights into localization phenomena and introduces a method to measure the single-particle density of states in the strong localization regime.

Findings

Observation of the crossover from weak to strong localization with decreasing temperature.

Identification of a minimum in the density of states at the Fermi level due to Coulomb interactions.

Detection of exponential negative magnetoresistance related to localization length dependence.

Abstract

We report on the experimental study of electron transport in sub-micron-wide ''wires'' fabricated from Si $\delta $-doped GaAs. These quasi-one-dimensional (Q1D) conductors demonstrate the crossover from weak to strong localization with decreasing the temperature. On the insulating side of the crossover, the resistance has been measured as a function of temperature, magnetic field, and applied voltage for different values of the electron concentration, which was varied by applying the gate voltage. The activation temperature dependence of the resistance has been observed with the activation energy close to the mean energy spacing of electron states within the localization domain. The study of non-linearity of the current-voltage characteristics provides information on the distance between the critical hops which govern the resistance of Q1D conductors in the strong localization (SL) regime. We observe the exponentially strong negative magnetoresistance; this orbital magnetoresistance is due to the universal magnetic-field dependence of the localization length in Q1D conductors. The method of measuring of the single-particle density of states (DoS) in the SL regime has been suggested. Our data indicate that there is a minimum of DoS at the Fermi level due to the long-range Coulomb interaction.