Current Induced Excitations in Cu/Co/Cu Single Ferromagnetic Layer Nanopillars

Current-induced magnetic excitations in Cu/Co/Cu single layer nanopillars (~50 nm in diameter) have been studied experimentally as a function of Co layer thickness at low temperatures for large applied fields perpendicular to the layers. For asymmetric junctions current induced excitations are observed at high current densities for only one polarity of the current and are absent at the same current densities in symmetric junctions. These observations confirm recent predictions of spin-transfer torque induced spin wave excitations in single layer junctions with a strong asymmetry in the spin accumulation in the leads.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Baryon stopping and hyperon enhancement in the improved dual parton model

We present an improved version of the dual parton model which contains a new realization of the diquark breaking mechanism of baryon stopping. We reproduce in this way the net baryon yield in nuclear collisions. The model, which also considers strings originating from diquark-antidiquark pairs in the nucleon sea, reproduces the observed yields of p and Lambda and their antiparticles and underestimates cascades by less than 50 %. However, Omega's are underestimated by a factor five. Agreement with data is restored by final state interaction, with an averaged cross-section as small as 0.14 mb. Hyperon yields increase significantly faster than antihyperons, in agreement with experiment.Comment: 40 pages, 18 postscript figure

Thermal Hadron Production in High Energy Heavy Ion Collisions

We provide a method to test if hadrons produced in high energy heavy ion collisions were emitted at freeze-out from an equilibrium hadron gas. Our considerations are based on an ideal gas at fixed temperature $T_f$, baryon number density $n_B$, and vanishing total strangeness. The constituents of this gas are all hadron resonances up to a mass of 2 GeV; they are taken to decay according to the experimentally observed branching ratios. The ratios of the various resulting hadron production rates are tabulated as functions of $T_f$ and $n_B$. These tables can be used for the equilibration analysis of any heavy ion data; we illustrate this for some specific cases.Comment: 12 pages (not included :13 figures + tables) report CERN-TH 6523/92 and Bielefeld preprint BI-TP 92/0

Interfacial charge transfer in nanoscale polymer transistors

Interfacial charge transfer plays an essential role in establishing the relative alignment of the metal Fermi level and the energy bands of organic semiconductors. While the details remain elusive in many systems, this charge transfer has been inferred in a number of photoemission experiments. We present electronic transport measurements in very short channel ($L < 100$ nm) transistors made from poly(3-hexylthiophene) (P3HT). As channel length is reduced, the evolution of the contact resistance and the zero-gate-voltage conductance are consistent with such charge transfer. Short channel conduction in devices with Pt contacts is greatly enhanced compared to analogous devices with Au contacts, consistent with charge transfer expectations. Alternating current scanning tunneling microscopy (ACSTM) provides further evidence that holes are transferred from Pt into P3HT, while much less charge transfer takes place at the Au/P3HT interface.Comment: 19 preprint pages, 6 figure

A user-centric system architecture for residential energy consumption reduction

Long-term energy consumption reduction can be achieved more readily through sensible cooperation between end users and technological advancements. The DANCER project presented here proposes a user-centric residential energy management system, with the intention to achieve long-term energy related behavioural changes, thus improving the energy efficiency of modern homes. Although, it follows the same basic principles as other contemporary approaches, it focuses on minimizing the interaction of the user with the system. This is achieved through an improved feedback mechanism and a generic, policy based service that takes advantage of the modularity and generality of the software architecture. The proposed system is designed to support a variety of technologies (WiFi, Zigbee, X10), in order to ameliorate the input and output of the decision making operation. In this paper, the general outline of the DANCER system architecture and its most important components are discussed and the prototype test-bed is presented. Special consideration is given to the implementation, operation and response behaviour of the prototype

Short-Range Interactions and Scaling Near Integer Quantum Hall Transitions

We study the influence of short-range electron-electron interactions on scaling behavior near the integer quantum Hall plateau transitions. Short-range interactions are known to be irrelevant at the renormalization group fixed point which represents the transition in the non-interacting system. We find, nevertheless, that transport properties change discontinuously when interactions are introduced. Most importantly, in the thermodynamic limit the conductivity at finite temperature is zero without interactions, but non-zero in the presence of arbitrarily weak interactions. In addition, scaling as a function of frequency, $\omega$, and temperature, $T$, is determined by the scaling variable $\omega/T^p$ (where $p$ is the exponent for the temperature dependence of the inelastic scattering rate) and not by $\omega/T$, as it would be at a conventional quantum phase transition described by an interacting fixed point. We express the inelastic exponent, $p$, and the thermal exponent, $z_T$, in terms of the scaling dimension, $-\alpha < 0$, of the interaction strength and the dynamical exponent $z$ (which has the value $z=2$), obtaining $p=1+2\alpha/z$ and $z_T=2/p$.Comment: 9 pages, 4 figures, submitted to Physical Review

Anti-Hyperon Enhancement through Baryon Junction Loops

The baryon junction exchange mechanism recently proposed to explain valence baryon number transport in nuclear collisions is extended to study midrapidity anti-hyperon production. Baryon junction-anti-junction (J anti-J) loops are shown to enhance anti-Lambda, anti-Xi, anti-Omega yields as well as lead to long range rapidity correlations. Results are compared to recent WA97 Pb + Pb -> Y + anti-Y + X data.Comment: 10 pages, 4 figure

Scaling in the Integer Quantum Hall Effect: interactions and low magnetic fields

Recent developments in the scaling theory of the integer quantum Hall effect are discussed. In particular, the influence of electron-electron interactions on the critical behavior are studied. It is further argued that recent experiments on the disappearance of the quantum Hall effect at low magnetic fields support rather than disprove the scaling theory, when interpreted properly.Comment: 13 pages, invited talk at DPG spring meeting, Regensburg, March 2000, to appear in Advances in Solid State Physics, ed. B. Krame

Configuration Mixing within the Energy Density Functional Formalism: Removing Spurious Contributions from Non-Diagonal Energy Kernels

Multi-reference calculations along the lines of the Generator Coordinate Method or the restoration of broken symmetries within the nuclear Energy Density Functional (EDF) framework are becoming a standard tool in nuclear structure physics. These calculations rely on the extension of a single-reference energy functional, of the Gogny or the Skyrme types, to non-diagonal energy kernels. There is no rigorous constructive framework for this extension so far. The commonly accepted way proceeds by formal analogy with the expressions obtained when applying the generalized Wick theorem to the non-diagonal matrix element of a Hamilton operator between two product states. It is pointed out that this procedure is ill-defined when extended to EDF calculations as the generalized Wick theorem is taken outside of its range of applicability. In particular, such a procedure is responsible for the appearance of spurious divergences and steps in multi-reference EDF energies, as was recently observed in calculations restoring particle number or angular momentum. In the present work, we give a formal analysis of the origin of this problem for calculations with and without pairing, i.e. constructing the density matrices from either Slater determinants or quasi-particle vacua. We propose a correction to energy kernels that removes the divergences and steps, and which is applicable to calculations based on any symmetry restoration or generator coordinate. The method is formally illustrated for particle number restoration and is specified to configuration mixing calculations based on Slater determinants.Comment: 27 pages, 1 figure, accepted for publication in PR