Imaging a Coupled Quantum Dot - Quantum Point Contact System

We performed measurements on a quantum dot and a capacitively coupled quantum point contact by using the sharp metallic tip of a low-temperature scanning force microscope as a scanned gate. The quantum point contact served as a detector for charges on the dot or nearby. It allowed us to distinguish single electron charging events in several charge traps from charging events on the dot. We analyzed the tip-induced potential quantitatively and found its shape to be independent of the voltage applied to the tip within a certain range of parameters. We estimate that the trap density is below 0.1% of the doping density and that the interaction energy between the quantum dot and a trap is a significant portion of the dot's charging energy. Possibly, such charge traps are the reason for frequently observed parametric charge rearrangements.Comment: 6 pages, 5 figure

In Situ Treatment of a Scanning Gate Microscopy Tip

In scanning gate microscopy, where the tip of a scanning force microscope is used as a movable gate to study electronic transport in nanostructures, the shape and magnitude of the tip-induced potential are important for the resolution and interpretation of the measurements. Contaminations picked up during topography scans may significantly alter this potential. We present an in situ high-field treatment of the tip that improves the tip-induced potential. A quantum dot was used to measure the tip-induced potential.Comment: 3 pages, 1 figure, minor changes to fit published versio

Measurement of the Tip-Induced Potential in Scanning Gate Experiments

We present a detailed experimental study on the electrostatic interaction between a quantum dot and the metallic tip of a scanning force microscope. Our method allowed us to quantitatively map the tip-induced potential and to determine the spatial dependence of the tip's lever arm with high resolution. We find that two parts of the tip-induced potential can be distinguished, one that depends on the voltage applied to the tip and one that is independent of this voltage. The first part is due to the metallic tip while we interpret the second part as the effect of a charged dielectric particle on the tip. In the measurements of the lever arm we find fine structure that depends on which quantum state we study. The results are discussed in view of scanning gate experiments where the tip is used as a movable gate to study nanostructures.Comment: 7 pages, 5 figures, minor changes to fit published versio

Imaging Coulomb Islands in a Quantum Hall Interferometer

In the Quantum Hall regime, near integer filling factors, electrons should only be transmitted through spatially-separated edge states. However, in mesoscopic systems, electronic transmission turns out to be more complex, giving rise to a large spectrum of magnetoresistance oscillations. To explain these observations, recent models put forward that, as edge states come close to each other, electrons can hop between counterpropagating edge channels, or tunnel through Coulomb islands. Here, we use scanning gate microscopy to demonstrate the presence of quantum Hall Coulomb islands, and reveal the spatial structure of transport inside a quantum Hall interferometer. Electron islands locations are found by modulating the tunneling between edge states and confined electron orbits. Tuning the magnetic field, we unveil a continuous evolution of active electron islands. This allows to decrypt the complexity of high magnetic field magnetoresistance oscillations, and opens the way to further local scale manipulations of quantum Hall localized states

NIKA: A millimeter-wave kinetic inductance camera

Current generation millimeter wavelength detectors suffer from scaling limits imposed by complex cryogenic readout electronics. To circumvent this it is imperative to investigate technologies that intrinsically incorporate strong multiplexing. One possible solution is the kinetic inductance detector (KID). In order to assess the potential of this nascent technology, a prototype instrument optimized for the 2 mm atmospheric window was constructed. Known as the N\'eel IRAM KIDs Array (NIKA), it was recently tested at the Institute for Millimetric Radio Astronomy (IRAM) 30-meter telescope at Pico Veleta, Spain. The measurement resulted in the imaging of a number of sources, including planets, quasars, and galaxies. The images for Mars, radio star MWC349, quasar 3C345, and galaxy M87 are presented. From these results, the optical NEP was calculated to be around $1 \times 10^{-15}$ W$/$Hz$^{1/2}$. A factor of 10 improvement is expected to be readily feasible by improvements in the detector materials and reduction of performance-degrading spurious radiation.Comment: Accepted for publication in Astronomy & Astrophysic

Lever arm of a metallic tip in scanning gate experiments

Abstract We present a scanning gate experiment on the electrostatic interaction between a semiconductor quantum dot and the metallic tip of a scanning force microscope. With the help of a feedback mechanism we can map the lever arm of the tip, using the quantum dot in a given quantum state as a sensitive electrometer. Besides the geometrically expected shape at length scales of hundreds of nanometers, we observe fine structure on much shorter length scales. r 2007 Elsevier B.V. All rights reserved. There are relatively few studies about an important factor common to all scanning gate experiments, namely the electrostatic potential that the tip induces in the sample. The importance of the tip potential for the interpretation of scanning gate measurements has been mentioned in some of the first studies [5] but only recently a technique was demonstrated allowing to determine it with high precision. In Ref. [6] we used a quantum dot as a very sensitive potentiometer to study the tip-induced potential. We demonstrated how, with the help of a feedback mechanism, one can map the tip potential with high spatial and energetical resolution. Additionally, we showed how the tip's lever arm on the quantum dot can be mapped and used to better understand the properties of the tip potential. In these measurements we found fine structure which illustrates how the scanning gate technique may yield local information about the quantum dot. Here we show a measurement reproducing the main findings. The measurement conditions were identical as in Ref. We used a quantum dot prepared on a GaAs/AlGaAs heterostructure with a two-dimensional electron gas residing 34 nm below the surface. The quantum dot was patterned by local anodic oxidation of the GaAs surface at room temperature. Subsequently, we evaporated a thin Ti film on the sample surface and this film was again patterned by local anodic oxidation We scanned the SFM tip at a constant height of about 200 nm over the sample surface. The dot was tuned into the Coulomb blockade regime, and we used a feedback mechanism to apply a voltage to a plunger gate such that one of the quantized energy levels of the dot always stayed in resonance with the chemical potential of the source and drain leads. The voltage on the plunger gate corresponds to the tip potential and with this technique we could ensure ARTICLE IN PRESS www.elsevier.com/locate/physe 1386-9477/$ -see front matter

Composition, structure and ecological importance of the Moraceae in a residual forest of Ucayali, Peru

Las especies de la familia Moraceae tienen gran importancia económica, medicinal y ecológica en la Amazonía; sin embargo, existen escasos estudios sobre su diversidad y dinámica poblacional en los bosques residuales. El objetivo fue determinar la composición, estructura e importancia ecológica de las Moraceae en un bosque residual. El método aplicado fue el descriptivo y consistió en establecer 16 parcelas de 20 m × 50 m (0,10 ha), en un bosque residual de la subestación Alexánder von Humboldt, del Instituto Nacional de Innovación Agraria-INIA, Pucallpa, departamento de Ucayali, donde se evaluaron los individuos de hábito arbóreo o hemiepífito, con DAP ≥ 2,50 cm. La composición florística estuvo representada por 33 especies, distribuidas en 12 géneros; se encontró cinco especies no registradas para Ucayali. Estructuralmente, la familia estuvo representada por 138 individuos/ha con una distribución horizontal semejante a una “J” invertida irregular, sin embargo, existieron diferentes estructuras horizontales entre especies. Se determinó que el 85% de las especies se encontraban en la clase diamétrica I (2,50 a 9,99 cm), siendo la más abundante Pseudolmedia laevis (Ruiz & Pav.) J.F. Macbr. (41,88 individuos/ha); y las más dominantes fueron Brosimum utile (Kunth) Oken (1,71 m2 /ha) y Brosimum alicastrum subsp. bolivarense (Pittier) C.C.Berg (0,90 m2 / ha). Asimismo, P. laevis y B. utile fueron las de mayor importancia ecológica. La información de la presente investigación permitirá establecer una línea base, que puede ser utilizada para proponer el manejo de las Moraceae en bosques residuales del mismo ámbito de estudio

Hadron Energy Reconstruction for the ATLAS Calorimetry in the Framework of the Non-parametrical Method

This paper discusses hadron energy reconstruction for the ATLAS barrel prototype combined calorimeter (consisting of a lead-liquid argon electromagnetic part and an iron-scintillator hadronic part) in the framework of the non-parametrical method. The non-parametrical method utilizes only the known $e/h$ ratios and the electron calibration constants and does not require the determination of any parameters by a minimization technique. Thus, this technique lends itself to an easy use in a first level trigger. The reconstructed mean values of the hadron energies are within $\pm 1$ of the true values and the fractional energy resolution is $[(58\pm3)/\sqrt{E}+(2.5\pm0.3)$. The value of the $e/h$ ratio obtained for the electromagnetic compartment of the combined calorimeter is $1.74\pm0.04$ and agrees with the prediction that $e/h > 1.7$ for this electromagnetic calorimeter. Results of a study of the longitudinal hadronic shower development are also presented. The data have been taken in the H8 beam line of the CERN SPS using pions of energies from 10 to 300 GeV.Comment: 33 pages, 13 figures, Will be published in NIM

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011