Mechanical Mixing in Nonlinear Nanomechanical Resonators

Nanomechanical resonators, machined out of Silicon-on-Insulator wafers, are operated in the nonlinear regime to investigate higher-order mechanical mixing at radio frequencies, relevant to signal processing and nonlinear dynamics on nanometer scales. Driven by two neighboring frequencies the resonators generate rich power spectra exhibiting a multitude of satellite peaks. This nonlinear response is studied and compared to $n^{th}$-order perturbation theory and nonperturbative numerical calculations.Comment: 5 pages, 7 figure

Nanomechanical resonators operating as charge detectors in the nonlinear regime

We present measurements on nanomechanical resonators machined from Silicon-on-Insulator substrates. The resonators are designed as freely suspended Au/Si beams of lengths on the order of 1 - 4 um and a thickness of 200 nm. The beams are driven into nonlinear response by an applied modulation at radio frequencies and a magnetic field in plane. The strong hysteresis of the magnetomotive response allows sensitive charge detection by varying the electrostatic potential of a gate electrode.Comment: 8 pages, 6 figure

Lane reduction in driven 2d-colloidal systems through microchannels

The transport behavior of a system of gravitationally driven colloidal particles is investigated. The particle interactions are determined by the superparamagnetic behavior of the particles. They can thus be arranged in a crystalline order by application of an external magnetic field. Therefore the motion of the particles through a narrow channel occurs in well-defined lanes. The arrangement of the particles is perturbed by diffusion and the motion induced by gravity. Due to these combined influences a density gradient forms along the direction of motion of the particles. A reconfiguration of the crystal is observed leading to a reduction of the number of lanes. In the course of the lane reduction transition a local melting of the quasi-crystalline phase to a disordered phase and a subsequent crystallization along the motion of the particles is observed. This transition is characterized experimentally and using Brownian dynamics (BD) simulations.Comment: 4 pages, 4 figure

Electrochemical contrast switching between black and white appearance of gelatin-covered zinc

Zinc and its alloys are widely used in the surface protection of metallic structural materials. Thus, zinc is an interesting and relevant candidate material for preparing stimuli-responsive surfaces. In this work, the switching of the optical appearance of zinc between black and white by an applied electrode potential is demonstrated. The zinc surface was covered by gelatin films and subjected to cyclic voltammetry (CV) in a chloride-containing electrolyte which induced pitting corrosion on the zinc surface. Between the different parts of the CV cycles, a reversible change in optical appearance was observed. During the oxidative half-cycles, the surfaces appear white, and during the reductive half-cycles, the surfaces appear brown to black, i.e. dark. Surface characterisation by x-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy shows that the gelatin coating is slightly oxidised during intial stages of the process, but remains intact and present at the surface. Raman spectra prove the presence of ZnO at the interface. Surface analysis shows only minor differences in composition between the black and white surfaces. Based on the available characterisation data, the white appearance associated with anodic currents is attributed to the formation of a non-passivating ZnO. The black appearance associated with cathodic currents is attributed to reduction of surface-confined zinc species, including ZnO and Zn2+. The role of the gelatin is presumably to prevent diffusion of the dissolution products into solution by complex formation and by acting as a diffusion barrier; gelatin will also affect the morphology of the reduction products. A similar switching was observed when gelatin was added to chloride electrolyte; surface analysis showed gelatin adsorption in this case. The black/white switching may, e.g. be useful for surfaces self-indicating corrosion potentials of galvanised steel

Different types of integrability and their relation to decoherence in central spin models

We investigate the relation between integrability and decoherence in central spin models with more than one central spin. We show that there is a transition between integrability ensured by the Bethe ansatz and integrability ensured by complete sets of commuting operators. This has a significant impact on the decoherence properties of the system, suggesting that it is not necessarily integrability or nonintegrability which is related to decoherence, but rather its type or a change from integrability to nonintegrability.Comment: 4 pages, 3 figure

A nanomechanical resonator shuttling single electrons at radio frequencies

We observe transport of electrons through a metallic island on the tip of a nanomechanical pendulum. The resulting tunneling current shows distinct features corresponding to the discrete mechanical eigenfrequencies of the pendulum. We report on measurements covering the temperature range from 300 K down to 4.2 K. We explain the I-V curve, which differs from previous theoretical predictions, with model calculations based on a Master equation approach.Comment: 5 pages, 4 jpeg-figure

Influence of chopped laser light onto the electronic transport through atomic-sized contacts

This article reports on the influence of laser irradiation onto the electrical conductance of gold nanocontacts established with the mechanically controllable breakjunction technique (MCB). We concentrate here on the study of reversible conductance changes which can be as high as 200%. We investigate the dependence on the initial conductance of the contacts, the wavelength, the intensity and position of the laser spot with respect to the sample. Under most conditions an enhancement of the conductance is observed. We discuss several physical mechanisms which might contribute to the observed effect including thermal expansion, rectification and photon-assisted transport. We conclude that thermal expansion is not the dominating one.Comment: 20 pages with 7 figures; conference contribution on the 9th near field optics conference 2006 in Lausanne, Switzerland; accepted by the Journal of Microscop

Mechanical Cooper pair transportation as a source of long distance superconducting phase coherence

Transportation of Cooper-pairs by a movable single Cooper-pair-box placed between two remote superconductors is shown to establish coherent coupling between them. This coupling is due to entanglement of the movable box with the leads and is manifested in the supression of quantum fluctuations of the relative phase of the order parameters of the leads. It can be probed by attaching a high resistance Josephson junction between the leads and measuring the current through this junction. The current is suppressed with increasing temperature.Comment: 4 pages, 4 figures, RevTeX; Updated version, typos correcte

Freedom from Obscenity

Interest in obscenity laws, in the reason and purpose for their being, their efficacy in achieving the ends for which they are intended, the threat their existence and enforcement pose to the freedoms of speech and press, and the attitude of the courts toward them, seems to be at a new high. Obscenity is universally condemned throughout the United States. Yet law enforcement officers who attempt to enforce obscenity laws invariably are accused of censoring and book burning. \u27 A good many of such charges come from persons whose ox is being gored-persons who have a pecuniary interest in having obscenity laws ignored rather than enforced. However, such charges also come from well-intentioned individuals who sincerely believe that criminal prosecutions for the dissemination of obscenity are a threat to individual freedoms. The purpose of this article is to discuss obscenity laws from a propitious point of view, pointing out the sound basis for their existence and enforcement, and examining some of the arguments made against them