On the temperature dependence of ballistic Coulomb drag in nanowires

We have investigated within the theory of Fermi liquid dependence of Coulomb drag current in a passive quantum wire on the applied voltage $V$ across an active wire and on the temperature $T$ for any values of $eV/k_BT$. We assume that the bottoms of the 1D minibands in both wires almost coincide with the Fermi level. We come to conclusions that 1) within a certain temperature interval the drag current can be a descending function of the temperature $T$; 2) the experimentally observed temperature dependence $T^{-0.77}$ of the drag current can be interpreted within the framework of Fermi liquid theory; 3) at relatively high applied voltages the drag current as a function of the applied voltage saturates; 4) the screening of the electron potential by metallic gate electrodes can be of importance.Comment: 7 pages, 1 figur

Phonon drag in ballistic quantum wires

The acoustic phonon-mediated drag-contribution to the drag current created in the ballistic transport regime in a one-dimensional nanowire by phonons generated by a current-carrying ballistic channel in a nearby nanowire is calculated. The threshold of the phonon-mediated drag current with respect to bias or gate voltage is predicted.Comment: 5 pages, 2 figure

Possible origin of the 0.5 plateau in the ballistic conductance of quantum point contacts

A non-equilibrium Green function formalism (NEGF) is used to study the conductance of a side-gated quantum point contact (QPC) in the presence of lateral spin-orbit coupling (LSOC). A small difference of bias voltage between the two side gates (SGs) leads to an inversion asymmetry in the LSOC between the opposite edges of the channel. In single electron modeling of transport, this triggers a spontaneous but insignificant spin polarization in the QPC. However, the spin polarization of the QPC is enhanced substantially when the effect of electron-electron interaction is included. The spin polarization is strong enough to result in the occurrence of a conductance plateau at 0.5G0 (G0 = 2e2/h) in the absence of any external magnetic field. In our simulations of a model QPC device, the 0.5 plateau is found to be quite robust and survives up to a temperature of 40K. The spontaneous spin polarization and the resulting magnetization of the QPC can be reversed by flipping the polarity of the source to drain bias or the potential difference between the two SGs. These numerical simulations are in good agreement with recent experimental results for side-gated QPCs made from the low band gap semiconductor InAs

Shot noise of Coulomb drag current

We work out a theory of shot noise in a special case. This is a noise of the Coulomb drag current excited under the ballistic transport regime in a one-dimensional nanowire by a ballistic non-Ohmic current in a nearby parallel nanowire. We predict sharp oscillation of the noise power as a function of gate voltage or the chemical potential of electrons. We also study dependence of the noise on the voltage V across the driving wire. For relatively large values of V the noise power is proportional to V^2.Comment: 9 pages, 2 figure

An overview of the ciao multiparadigm language and program development environment and its design philosophy

We describe some of the novel aspects and motivations behind the design and implementation of the Ciao multiparadigm programming system. An important aspect of Ciao is that it provides the programmer with a large number of useful features from different programming paradigms and styles, and that the use of each of these features can be turned on and off at will for each program module. Thus, a given module may be using e.g. higher order functions and constraints, while another module may be using objects, predicates, and concurrency. Furthermore, the language is designed to be extensible in a simple and modular way. Another important aspect of Ciao is its programming environment, which provides a powerful preprocessor (with an associated assertion language) capable of statically finding non-trivial bugs, verifying that programs comply with specifications, and performing many types of program optimizations. Such optimizations produce code that is highly competitive with other dynamic languages or, when the highest levéis of optimization are used, even that of static languages, all while retaining the interactive development environment of a dynamic language. The environment also includes a powerful auto-documenter. The paper provides an informal overview of the language and program development environment. It aims at illustrating the design philosophy rather than at being exhaustive, which would be impossible in the format of a paper, pointing instead to the existing literature on the system

Ballistic electron transport in stubbed quantum waveguides: experiment and theory

We present results of experimental and theoretical investigations of electron transport through stub-shaped waveguides or electron stub tuners (ESTs) in the ballistic regime. Measurements of the conductance G as a function of voltages, applied to different gates V_i (i=bottom, top, and side) of the device, show oscillations in the region of the first quantized plateau which we attribute to reflection resonances. The oscillations are rather regular and almost periodic when the height h of the EST cavity is small compared to its width. When h is increased, the oscillations become less regular and broad depressions in G appear. A theoretical analysis, which accounts for the electrostatic potential formed by the gates in the cavity region, and a numerical computation of the transmission probabilities successfully explains the experimental observations. An important finding for real devices, defined by surface Schottky gates, is that the resonance nima result from size quantization along the transport direction of the EST.Comment: Text 20 pages in Latex/Revtex format, 11 Postscript figures. Phys. Rev. B,in pres

User-definable resource bounds analysis for logic programs

We present a static analysis that infers both upper and lower bounds on the usage that a logic program makes of a set of user-definable resources. The inferred bounds will in general be functions of input data sizes. A resource in our approach is a quite general, user-defined notion which associates a basic cost function with elementary operations. The analysis then derives the related (upper- and lower-bound) resource usage functions for all predicates in the program. We also present an assertion language which is used to define both such resources and resourcerelated properties that the system can then check based on the results of the analysis. We have performed some preliminary experiments with some concrete resources such as execution steps, bytes sent or received by an application, number of files left open, number of accesses to a datábase, number of calis to a procedure, number of asserts/retracts, etc. Applications of our analysis include resource consumption verification and debugging (including for mobile code), resource control in parallel/distributed computing, and resource-oriented specialization

Closed form solution for a double quantum well using Gr\"obner basis

Analytical expressions for spectrum, eigenfunctions and dipole matrix elements of a square double quantum well (DQW) are presented for a general case when the potential in different regions of the DQW has different heights and effective masses are different. This was achieved by Gr\"obner basis algorithm which allows to disentangle the resulting coupled polynomials without explicitly solving the transcendental eigenvalue equation.Comment: 4 figures, Mathematica full calculation noteboo