Electron turbulence at nanoscale junctions

Electron transport through a nanostructure can be characterized in part using concepts from classical fluid dynamics. It is thus natural to ask how far the analogy can be taken, and whether the electron liquid can exhibit nonlinear dynamical effects such as turbulence. Here we present an ab-initio study of the electron dynamics in nanojunctions which reveals that the latter indeed exhibits behavior quite similar to that of a classical fluid. In particular, we find that a transition from laminar to turbulent flow occurs with increasing current, corresponding to increasing Reynolds numbers. These results reveal unexpected features of electron dynamics and shed new light on our understanding of transport properties of nanoscale systems.Comment: 5 pages, 3 figure

Approach to steady state transport in nanoscale conductors

We show, using a tight-binding model and time-dependent density-functional theory, that a quasi-steady state current can be established dynamically in a finite nanoscale junction without any inelastic effects. This is simply due to the geometrical constriction experienced by the electron wavepackets as they propagate through the junction. We also show that in this closed non-equilibrium system two local electron occupation functions can be defined on each side of the nanojunction which approach Fermi distributions with increasing number of atoms in the electrodes. The resultant conductance and current-voltage characteristics at quasi-steady state are in agreement with those calculated within the static scattering approach.Comment: 4+ pages in REVTEX4, 4 epsf figure

The decay of excited He from Stochastic Density-Functional Theory: a quantum measurement theory interpretation

Recently, time-dependent current-density functional theory has been extended to include the dynamical interaction of quantum systems with external environments [Phys. Rev. Lett. {\bf 98}, 226403 (2007)]. Here we show that such a theory allows us to study a fundamentally important class of phenomena previously inaccessible by standard density-functional methods: the decay of excited systems. As an example we study the decay of an ensemble of excited He atoms, and discuss these results in the context of quantum measurement theory.Comment: 4 pages, 2 figure

Microscopic Current Dynamics in Nanoscale Junctions

So far transport properties of nanoscale contacts have been mostly studied within the static scattering approach. The electron dynamics and the transient behavior of current flow, however, remain poorly understood. We present a numerical study of microscopic current flow dynamics in nanoscale quantum point contacts. We employ an approach that combines a microcanonical picture of transport with time-dependent density-functional theory. We carry out atomic and jellium model calculations to show that the time evolution of the current flow exhibits several noteworthy features, such as nonlaminarity and edge flow. We attribute these features to the interaction of the electron fluid with the ionic lattice, to the existence of pressure gradients in the fluid, and to the transient dynamical formation of surface charges at the nanocontact-electrode interfaces. Our results suggest that quantum transport systems exhibit hydrodynamical characteristics which resemble those of a classical liquid.Comment: 8 pages, 5 figures; Accepted for publication in Phys. Rev.

Electron dynamics in nanoscale systems

In this dissertation we discuss the dynamical behavior of electrons on the nanoscopic scale. We begin by presenting a view of electron transport which an alternative to that due to Landauer, in which the flow of electrons across a junction is framed as the discharge of a large but finite capacitor. The benefit of this construction is that time- dependent calculations can be framed in a conceptually simple and well-defined way. We characterize the conductance of a quasi-one-dimensinal chain of gold atoms, as well as a quantity which is similar to the distribution functions of classical statistical mechanics. We go on to the quasi-two-dimensional case and characterize the flow patterns of electrons emerging from a nanoscopic junction. We discuss the dynamic angular pattern of electron flow, as well as the movement of charge at the surface of the electrodes near the junction. We continue by considering the hydrodynamic form of the many-body Schrödinger equation and demonstrate that the electron liquid develops turbulent eddy-like structures in experimentally attainable regimes. We provide the demonstration using both an ab-initio formalism, as well as an approximate Navier-Stokes calculation. We go on to describe an experiment whereby the turbulence of the electron liquid could be detected through the use of a Superconducting Quantum Interference Device (SQUID), by measuring the asymmetry in the magnetic flux produced as a result of current flow near the nanoscopic junction. In addition, we characterize the turbulent eddies by considering the velocity correlation tensor Finally, we discuss the stochastic extension to current density functional theory and demonstrate the decay of a Helium atom which is effectively coupled to an external reservoir. We demonstrate the utility of the stochastic Schrödinger formalism as compared to the master equation approach, and discuss the relevance of the stochastic Shrödinger equation to quantum measurement theor

Systemic Insecticide Applications at Planting for Early Season Thrips Control

Temik 15G (6 lbs/acre) or Thimet 20G (8.2 lbs/acre) granular insecticides were applied to 40 inch rows in furrow at planting to cotton growing in Parker Valley, AZ. Moderate thrips pressure (0.5-1.5 thrips/plant) was experienced for the first eight weeks after planting and granular insecticide application. Temik provided better thrips control than Thimet for the first seven weeks after planting this study. Thrips control was similar for the two insecticides beyond eight weeks after planting. Temik application resulted in higher fruit retention levels measured up to 10 weeks after planting, compared to Thimet. However, fruit retention levels measured from 12 to 16 weeks after planting were similar for both Temik and Thimet when cotton plants compensated for early season square losses caused by thrips feeding