Urbaszek B.,INSA Toulouse |
Marie X.,INSA Toulouse |
Amand T.,INSA Toulouse |
Krebs O.,CNRS Laboratory for Photonics and Nanostructures |
And 4 more authors.
Reviews of Modern Physics | Year: 2013
The mesoscopic spin system formed by the 104-106 nuclear spins in a semiconductor quantum dot offers a unique setting for the study of many-body spin physics in the condensed matter. The dynamics of this system and its coupling to electron spins is fundamentally different from its bulk counterpart or the case of individual atoms due to increased fluctuations that result from reduced dimensions. In recent years, the interest in studying quantum-dot nuclear spin systems and their coupling to confined electron spins has been further fueled by its importance for possible quantum information processing applications. The fascinating nonlinear (quantum) dynamics of the coupled electron-nuclear spin system is universal in quantum dot optics and transport. In this article, experimental work performed over the last decade in studying this mesoscopic, coupled electron-nuclear spin system is reviewed. Here a special focus is on how optical addressing of electron spins can be exploited to manipulate and read out the quantum-dot nuclei. Particularly exciting recent developments in applying optical techniques to efficiently establish nonzero mean nuclear spin polarizations and using them to reduce intrinsic nuclear spin fluctuations are discussed. Both results critically influence the preservation of electron-spin coherence in quantum dots. This overall recently gained understanding of the quantum-dot nuclear spin system could enable exciting new research avenues such as experimental observations of spontaneous spin ordering or nonclassical behavior of the nuclear spin bath. © 2013 American Physical Society.
Dubrovskii V.G.,RAS Ioffe Physical - Technical Institute |
Cirlin G.E.,RAS Ioffe Physical - Technical Institute |
Sibirev N.V.,St Petersburg Academic University |
Jabeen F.,CNRS Laboratory for Photonics and Nanostructures |
And 2 more authors.
Nano Letters | Year: 2011
We report on the new mode of the vapor-liquid-solid nanowire growth with a droplet wetting the sidewalls and surrounding the nanowire rather than resting on its top. It is shown theoretically that such an unusual configuration happens when the growth is catalyzed by a lower surface energy metal. A model of a nonspherical elongated droplet shape in the wetting case is developed. Theoretical predictions are compared to the experimental data on the Ga-catalyzed growth of GaAs nanowires by molecular beam epitaxy. In particular, it is demonstrated that the experimentally observed droplet shape is indeed nonspherical. The new VLS mode has a major impact on the crystal structure of GaAs nanowires, helping to avoid the uncontrolled zinc blende-wurtzite polytylism under optimized growth conditions. Since the triple phase line nucleation is suppressed on surface energetic grounds, all nanowires acquire pure zinc blende phase along the entire length, as demonstrated by the structural studies of our GaAs nanowires. © 2011 American Chemical Society.
Luais B.,University of Lorraine |
Luais B.,CNRS Laboratory for Photonics and Nanostructures
Chemical Geology | Year: 2013
Chemical separation and isotopic measurement of germanium using hexapole-collision cell-MC-ICPMS were developed in various Fe-Ni, ZnS and silicates matrices in order to investigate the potentiality of Ge as an isotopic tracer of planetary differentiation and rock-forming processes. Analytical procedures are described for the critical step of silicate dissolution in HF+HNO3 medium, as well as for Ge chemical purification using a single cationic-exchange resin step for Fe-Ni and ZnS matrices, and two anionic and cationic resin steps for silicate matrices. Germanium isotopic measurements using MC-ICPMS were performed with appropriate Ar+H fluxes in the collision cell to eliminate argide interferences on Ge masses. Three methods of mass bias correction, including sample standard bracketing, external Ga mass bias correction using the exponential law, and the empirical "regression method", give similar results and demonstrate the use of Ga as an appropriate element for mass bias correction of Ge. Results are presented as delta values with respect to JMC Ge standard, and NIST3120a Ge standard for comparison. We show a long-term 2SD reproducibility of less than 0.24% on the δ74Ge.These analytical methods have been applied to Fe-meteorites, sphalerite (ZnS) deposits, and geostandard silicates ranging from ultramafic to basaltic to granitic compositions, and to an iron formation composition. Fe-meteorites and terrestrial silicate samples display small variations of δ74GeJMC=+1.77±0.22% and +0.89±0.16% (2SD reproducibility), respectively. This contrasts with the large variations seen in low-temperature rocks, such as the ZnS ores (δ74GeJMC=-0.37 to -1.69%), and banded iron formations (IF-G Isua, δ74GeJMC=+1.38%). A slight δ74GeJMC-NBO/T negative tendency in silicate samples indicates that polymerisation of silicate melt would control the small Ge isotope fractionation among mantle silicates.A comparison of δ74Ge values of iron meteorites and Earth silicate mantle opens new perspectives in deep Earth processes. On the basis of theoretical metal-silicate isotopic equilibrium processes, the low δ74Ge of silicate Earth cannot reconcile one-stage process of core-mantle segregation. It is proposed that the δ74Ge(JMC) value of silicate earth samples of +0.89±0.16% (or δ74Ge(NIST3120a)=+0.53%) represents the composition of the accessible Earth modern mantle. The δ74Ge of the silicate mantle in equilibrium with the core at time of core formation would be distinct to that of the present mantle in result of distinct thermodynamic parameters, e.g. fO2, pressure, inducing changes in coordination and valence state of Ge in the silicate crystallographic structure. In addition, the light isotopic composition of the Earth's mantle could result from reverse diffusive processes induced by an increase in oxidation state at the end of core formation. This would have some implications on core formation modelling and the use of Ge isotopes for tracing the origin of deep mantle plumes. © 2012 Elsevier B.V.
Somaschi N.,CNRS Laboratory for Photonics and Nanostructures
Nature Photonics | Year: 2016
The scaling of optical quantum technologies requires efficient, on-demand sources of highly indistinguishable single photons. Semiconductor quantum dots inserted into photonic structures are ultrabright single-photon sources, yet the indistinguishability is limited by charge noise. Parametric downconversion sources provide highly indistinguishable photons but are operated at very low brightness to maintain high single-photon purity. To date, no technology has provided a bright source generating near-unity indistinguishability and pure single photons. Here, we report such devices made of quantum dots in electrically controlled cavities. Application of an electrical bias on the deterministically fabricated structures is shown to strongly reduce charge noise. Under resonant excitation, an indistinguishability of 0.9956 ± 0.0045 is demonstrated with g(2)(0) = 0.0028 ± 0.0012. The photon extraction of 65% and measured brightness of 0.154 ± 0.015 make this source 20 times brighter than any source of equal quality. This new generation of sources opens the way to new levels of complexity and scalability in optical quantum technologies. © 2016 Nature Publishing Group
Armitano J.,CNRS Laboratory for Photonics and Nanostructures
Research in microbiology | Year: 2011
Bacteria, and in particular marine bacteria, can be found in environments that are poor in nutrients. To survive, they are able to move toward more favorable niches by a mechanism called chemotaxis, whose first step consists in the detection of substrates by chemoreceptors. We developed a chemotactic assay enabling rapid testing of several hundred different solutes and we identified several molecules eliciting a chemotactic response from two aquatic Shewanella species. We propose that this assay be used for other bacteria to determine the repertoire of chemotactic molecules, generally not clearly elucidated. Copyright © 2011 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.
Glas F.,CNRS Laboratory for Photonics and Nanostructures |
Harmand J.-C.,CNRS Laboratory for Photonics and Nanostructures |
Patriarche G.,CNRS Laboratory for Photonics and Nanostructures
Physical Review Letters | Year: 2010
We elaborate InP1-xAsx nanowires by vapor-liquid-solid growth, with small and short composition oscillations produced on purpose with a constant time period. The lengths of these oscillations, measured in single wires by transmission electron microscopy, give access to instantaneous growth rates and their distribution reveals the nucleation statistics. We find that these statistics are strongly sub-Poissonian, which proves that the nucleation events are anticorrelated in time. This effect, specific to nanovolumes, efficiently regulates nanowire growth. We explain it by the rapid depletion of the catalyst droplet in group V atoms upon forming each monolayer of the nanowire. © 2010 The American Physical Society.
Priante G.,CNRS Laboratory for Photonics and Nanostructures |
Patriarche G.,CNRS Laboratory for Photonics and Nanostructures |
Oehler F.,CNRS Laboratory for Photonics and Nanostructures |
Glas F.,CNRS Laboratory for Photonics and Nanostructures |
Harmand J.-C.,CNRS Laboratory for Photonics and Nanostructures
Nano Letters | Year: 2015
We achieve the self-catalyzed growth of pure GaP nanowires and GaAs1-xPx/GaAs1-yPy nanowire heterostructures by solid-source molecular beam epitaxy. Consecutive segments of nearly pure GaAs and GaP are fabricated by commuting the group V fluxes. We test different flux switching procedures and measure the corresponding interfacial composition profiles with atomic resolution using high-angle annular dark field scanning transmission electron microscopy. Interface abruptness is drastically improved by switching off all the molecular beam fluxes for a short time at the group V commutation. Finally, we demonstrate that the morphology of the growth front can be either flat or truncated, depending on the growth conditions. The method presented here allows for the facile synthesis of high quality GaP/GaAs axial heterostructures directly on Si (111) wafers. © 2015 American Chemical Society.
Krebs O.,CNRS Laboratory for Photonics and Nanostructures |
Lemaitre A.,CNRS Laboratory for Photonics and Nanostructures
Physical Review Letters | Year: 2013
We report evidence of a photoinduced coupling between two spins provided by Mn dopants in their neutral acceptor state A0 in a single InAs/GaAs quantum dot. The coupling occurs due to simultaneous exchange interactions between each of the two dopant spins and a photocreated hole. Microphotoluminescence spectroscopy achieved both in longitudinal and perpendicular magnetic fields reveals the splitting of the four spin configurations |J1=±1, J2=±1〉 due to the 2A0-hole exchange interaction. We obtain a comprehensive interpretation of the experimental data with a simplified spin Hamiltonian model, which more specifically shows that the hole-mediated coupling is similar to a ε12â‰-70 μeV exchange interaction between both A0 spins. © 2013 American Physical Society.
Collin S.,CNRS Laboratory for Photonics and Nanostructures
Reports on Progress in Physics | Year: 2014
Dielectric and metallic gratings have been studied for more than a century. Nevertheless, novel optical phenomena and fabrication techniques have emerged recently and have opened new perspectives for applications in the visible and infrared domains. Here, we review the design rules and the resonant mechanisms that can lead to very efficient light-matter interactions in sub-wavelength nanostructure arrays. We emphasize the role of symmetries and free-space coupling of resonant structures. We present the different scenarios for perfect optical absorption, transmission or reflection of plane waves in resonant nanostructures. We discuss the fabrication issues, experimental achievements and emerging applications of resonant nanostructure arrays. © 2014 IOP Publishing Ltd.
Glas F.,CNRS Laboratory for Photonics and Nanostructures
Journal of Applied Physics | Year: 2010
For use in quantitatively modeling the growth of gold-seeded semiconductor nanowires in the vapor-liquid-solid mode, we calculate the difference of chemical potential between a liquid melt formed of group III and group V atoms dissolved in gold and the corresponding solid III-V binary compound. Fits to our results are provided for seven compounds as simple polynomials of the concentrations in the III-V-Au liquid and temperature. We find that the difference of chemical potential increases with the group III and group V concentrations, decreases with increasing temperature, and can easily reach several hundreds of meV per III-V pair. We discuss these values and variations in the light of published experimental results, in particular as regards the crystalline structure adopted by the nanowires during growth. © 2010 American Institute of Physics.