Universal conductance fluctuations in three dimensional metallic single crystals of Si

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_ϕ(L/L_ϕ\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_ϕ^3 was found to be saturated at <(δG_ϕ)^2> \approx (e^2/h)^2. An accurate knowledge of the level of disorder, enables us to calculate the change in conductance δG_1 due to movement of a single scatterer as δG_1 \sim e^2/h, which is \sim 2 orders of magnitude higher than its theoretically expected value in 3D systems.