Conductance Fluctuations In Metals Research Articles

Correlation Field Analysis of Magnetoresistance of GaN/AlGaN Heterostructure Grown on Si Substrate

We analyze the conductance fluctuations for a bulk two-dimensional electron system in a GaN/Al0.15Ga0.85N heterostructure grown on a p-type Si(111) substrate, and calculate the correlation field Bc with the autocorrelation function F(ΔB) = <δG(B + ΔB) - δG(B)>, in the temperature range 0.27 ≤T ≤3 K, which is employed as a self-thermometer to obtain the effective carrier temperature Te as a function of the measurement current I. We find that the temperature dependence agrees well with simple expectations for universal conductance fluctuations in metals, while the observed amplitude is reduced. In the study of hot-carrier phenomena, we also obtain Te ∼I0.5, which agrees with some theoretical prediction.

Conductance fluctuations at the quantum Hall plateau transition

We analyze the conductance fluctuations observed in the quantum Hall regime for a bulk two-dimensional electron system in a Corbino geometry. We find that characteristics like the power spectral density and the temperature dependence agree well with simple expectations for universal conductance fluctuations in metals, while the observed amplitude is reduced. In addition, the dephasing length ${L}_{\ensuremath{\Phi}}\ensuremath{\propto}{T}^{\ensuremath{-}1/2},$ which governs the temperature dependence of the fluctuations, is surprisingly different from the scaling length ${L}_{\mathrm{sc}}\ensuremath{\propto}{T}^{\ensuremath{-}1}$ governing the width of the quantum Hall plateau transition.

Universal fluctuations and long-range correlations for wave propagation in random media

The last few years, a large amount of effort has been devoted to the study of coherent effects in disordered systems. They essentially dealt with average values over a whole ensemble of samples and gave rise to the so-called coherent corrections of the weak localization regime. Recently, the transport properties of small disordered (mesoscopic) samples were considered from the view-point of the exact wave configuration (speckle pattern) of a given realization of the random impurity potential. A new kind of coherent effects appeared in the statistics of various properties of disordered samples like for example the universal conductance fluctuations in metals which are size-independent. These properties are shown to come from the long-range correlations in the fluctuations due to the underlying wave-field.

Intensity correlation functions and fluctuations in light scattered from a random medium.

The propagation of light in a disordered medium with purely elastic scattering is considered. The intensity correlation functions for the diffusely reflected and transmitted light from a slab are shown to have long-range power-law behavior. This arises from the interference of the underlying wave fields of the diffusive modes of the light intensity. This interference also gives rise to anomalous fluctuations in the transmission coefficient analogous to conductance fluctuations in metals.

Universal conductance fluctuations in metals: Effects of finite temperature, interactions, and magnetic field.

The conductance of any metallic sample has been shown to fluctuate as a function of chemical potential, magnetic field, or impurity configuration by an amount of order ${e}^{2}$/h independent of sample size and degree of disorder at zero temperature. We discuss the relationship of these results to other results in the theory of weak and strong localization, and discuss its physical implications. We discuss the physical assumptions underlying the ergodic hypothesis used to relate theory to experiment. We review the zero-temperature theory and provide a detailed discussion of the conductance correlation functions in magnetic field and Fermi energy. We show that the zero-temperature amplitude of the fluctuations is unaffected by electron-electron interactions to lowest order in (${k}_{f}$l${)}^{\mathrm{\ensuremath{-}}1}$, and at finite temperature interactions only enter insofar as they contribute to the inelastic scattering rate. We calculate the effects of finite temperature on both the amplitude of the fluctuations and their scale. We discuss the conditions for dimensional crossover at finite temperature, and the behavior of different experimental measures of the fluctuation amplitude, in order to facilitate quantitative comparisons of experiment and theory.

Quantum Transport and Fluctuations in Small Systems

A review of the theory of conductance fluctuations in metals at low temperatures is given, with emphasis on the intuitive understanding of the basic physics, and the rich variety of physical phenomena that have been uncovered upon entering the quantum regime.