Universal conductance fluctuations in three dimensional metallic single crystals of Si

TL;DR

This study measures universal conductance fluctuations in heavily doped silicon single crystals, revealing saturation of fluctuations and a higher-than-expected conductance change per scatterer in a truly three-dimensional system.

Contribution

It provides experimental evidence of UCF in 3D silicon crystals and quantifies conductance fluctuations and scatterer effects beyond theoretical predictions.

Findings

Conductance fluctuations saturate at (e^2/h)^2 in 3D silicon.

Change in conductance due to a single scatterer is about 100 times larger than expected.

Temperature and magnetic field dependence confirm UCF as the dominant noise source.

Abstract

In this paper we report the measurement of conductance fluctuations in single crystals of Si made metallic by heavy doping (n \approx 2-2.5n_c, n_c being critical composition at Metal-Insulator transition). Since all dimensions (L) of the samples are much larger than the electron phase coherent length L_\phi (L/L_\phi \sim 10^3), our system is truly three dimensional. Temperature and magnetic field dependence of noise strongly indicate the universal conductance fluctuations (UCF) as predominant source of the observed magnitude of noise. Conductance fluctuations within a single phase coherent region of L_\phi^3 was found to be saturated at <(\delta G_\phi)^2> \approx (e^2/h)^2. An accurate knowledge of the level of disorder, enables us to calculate the change in conductance \delta G_1 due to movement of a single scatterer as \delta G_1 \sim e^2/h, which is \sim 2 orders of magnitude higher than its theoretically expected value in 3D systems.