2D Rutherford-Like Scattering in Ballistic Nanodevices

Ballistic injection in a nanodevice is a complex process where electrons can either be transmitted or reflected, thereby introducing deviations from the otherwise quantized conductance. In this context, quantum rings (QRs) appear as model geometries: in a semiclassical view, most electrons bounce against the central QR antidot, which strongly reduces injection efficiency. Thanks to an analogy with Rutherford scattering, we show that a local partial depletion of the QR close to the edge of the antidot can counter-intuitively ease ballistic electron injection. On the contrary, local charge accumulation can focus the semi-classical trajectories on the hard-wall potential and strongly enhance reflection back to the lead. Scanning gate experiments on a ballistic QR, and simulations of the conductance of the same device are consistent, and agree to show that the effect is directly proportional to the ratio between the strength of the perturbation and the Fermi energy. Our observation surprisingly fits the simple Rutherford formalism in two-dimensions in the classical limit

Scanning Gate Spectroscopy of transport across a Quantum Hall Nano-Island

We explore transport across an ultra-small Quantum Hall Island (QHI) formed by closed quan- tum Hall edge states and connected to propagating edge channels through tunnel barriers. Scanning gate microscopy and scanning gate spectroscopy are used to first localize and then study a single QHI near a quantum point contact. The presence of Coulomb diamonds in the spectroscopy con- firms that Coulomb blockade governs transport across the QHI. Varying the microscope tip bias as well as current bias across the device, we uncover the QHI discrete energy spectrum arising from electronic confinement and we extract estimates of the gradient of the confining potential and of the edge state velocity.Comment: 13 pages, 3 figure

Formation of quantum dots in the potential fluctuations of InGaAs heterostructures probed by scanning gate microscopy

The disordered potential landscape in an InGaAs/InAlAs two-dimensional electron gas patterned into narrow wires is investigated by means of scanning gate microscopy. It is found that scanning a negatively charged tip above particular sites of the wires produces conductance oscillations that are periodic in the tip voltage. These oscillations take the shape of concentric circles whose number and diameter increase for more negative tip voltages until full depletion occurs in the probed region. These observations cannot be explained by charging events in material traps, but are consistent with Coulomb blockade in quantum dots forming when the potential fluctuations are raised locally at the Fermi level by the gating action of the tip. This interpretation is supported by simple electrostatic simulations in the case of a disorder potential induced by ionized dopants. This work represents a local investigation of the mechanisms responsible for the disorder-induced metal-to-insulator transition observed in macroscopic two-dimensional electron systems at low enough density

Scanning-gate microscopy of semiconductor nanostructures: an overview

This paper presents an overview of scanning-gate microscopy applied to the imaging of electron transport through buried semiconductor nanostructures. After a brief description of the technique and of its possible artifacts, we give a summary of some of its most instructive achievements found in the literature and we present an updated review of our own research. It focuses on the imaging of GaInAs-based quantum rings both in the low magnetic field Aharonov-Bohm regime and in the high-field quantum Hall regime. In all of the given examples, we emphasize how a local-probe approach is able to shed new, or complementary, light on transport phenomena which are usually studied by means of macroscopic conductance measurements.Comment: Invited talk by SH at 39th "Jaszowiec" International School and Conference on the Physics of Semiconductors, Krynica-Zdroj, Poland, June 201

Parity violation in radiative neutron capture on deuteron

Parity violating (PV) effects in neutron-deuteron radiative capture are studied using Desplanques, Donoghue, and Holstein (DDH) and effective field theory weak potentials. The values of PV effects are calculated using wave functions, obtained by solving three-body Faddeev equations in configuration space for phenomenological strong potentials. The relations between physical observables and low-energy constants are presented, and dependencies of the calculated PV effects on strong and weak potentials are discussed. The presented analysis shows the possible reason for the existing discrepancy in PV nuclear data analysis using the DDH approach and reveals a new opportunity to study short range interactions in nuclei

Parity violation in n+3He→3H+pn + ^3He \rightarrow ^3H + p reaction: resonance approach

The method based on microscopic theory of nuclear reactions has been applied for the analysis of parity violating effects in a few-body systems. Different parity violating and parity conserving asymmetries and their dependence on neutron energy have been estimated for $n + ^3He \rightarrow ^3H + p$ reaction. The estimated effects are in a good agreement with available exact calculations

Transport inefficiency in branched-out mesoscopic networks: An analog of the Braess paradox

We present evidence for a counter-intuitive behavior of semiconductor mesoscopic networks that is the analog of the Braess paradox encountered in classical networks. A numerical simulation of quantum transport in a two-branch mesoscopic network reveals that adding a third branch can paradoxically induce transport inefficiency that manifests itself in a sizable conductance drop of the network. A scanning-probe experiment using a biased tip to modulate the transmission of one branch in the network reveals the occurrence of this paradox by mapping the conductance variation as a function of the tip voltage and position.Comment: 2nd version with minor stylistic corrections. To appear in Phys. Rev. Lett.: Editorially approved for publication 6 January 201

Planning the electron traffic in semiconductor networks: A mesoscopic analog of the Braess paradox encountered in road networks

By combining quantum simulations of electron transport and scanning-gate microscopy, we have shown that the current transmitted through a semiconductor two-path rectangular network in the ballistic and coherent regimes of transport can be paradoxically degraded by adding a third path to the network. This is analogous to the Braess paradox occurring in classical networks. Simulations reported here enlighten the role played by congestion in the network.Comment: 31st Int. Conf. Phys. Semiconductors, Zurich, July-August 201

Structural and Content Diversity of Mitochondrial Genome in Beet: A Comparative Genomic Analysis

Despite their monophyletic origin, mitochondrial (mt) genomes of plants and animals have developed contrasted evolutionary paths over time. Animal mt genomes are generally small, compact, and exhibit high mutation rates, whereas plant mt genomes exhibit low mutation rates, little compactness, larger sizes, and highly rearranged structures. We present the (nearly) whole sequences of five new mt genomes in the Beta genus: four from Beta vulgaris and one from B. macrocarpa, a sister species belonging to the same Beta section. We pooled our results with two previously sequenced genomes of B. vulgaris and studied genome diversity at the species level with an emphasis on cytoplasmic male-sterilizing (CMS) genomes. We showed that, contrary to what was previously assumed, all three CMS genomes belong to a single sterile lineage. In addition, the CMSs seem to have undergone an acceleration of the rates of substitution and rearrangement. This study suggests that male sterility emergence might have been favored by faster rates of evolution, unless CMS itself caused faster evolution

Characterisation of sugar beet (Beta vulgaris L. ssp. vulgaris) varieties using microsatellite markers

<p>Abstract</p> <p>Background</p> <p>Sugar beet is an obligate outcrossing species. Varieties consist of mixtures of plants from various parental combinations. As the number of informative morphological characteristics is limited, this leads to some problems in variety registration research.</p> <p>Results</p> <p>We have developed 25 new microsatellite markers for sugar beet. A selection of 12 markers with high quality patterns was used to characterise 40 diploid and triploid varieties. For each variety 30 individual plants were genotyped. The markers amplified 3-21 different alleles. Varieties had up to 7 different alleles at one marker locus. All varieties could be distinguished. For the diploid varieties, the expected heterozygosity ranged from 0.458 to 0.744. The average inbreeding coefficient F_iswas 0.282 ± 0.124, but it varied widely among marker loci, from F_is= +0.876 (heterozygote deficiency) to F_is= -0.350 (excess of heterozygotes). The genetic differentiation among diploid varieties was relatively constant among markers (F_st= 0.232 ± 0.027). Among triploid varieties the genetic differentiation was much lower (F_st= 0.100 ± 0.010). The overall genetic differentiation between diploid and triploid varieties was F_st= 0.133 across all loci. Part of this differentiation may coincide with the differentiation among breeders' gene pools, which was F_st= 0.063.</p> <p>Conclusions</p> <p>Based on a combination of scores for individual plants all varieties can be distinguished using the 12 markers developed here. The markers may also be used for mapping and in molecular breeding. In addition, they may be employed in studying gene flow from crop to wild populations.</p