Séminaires "Nanoélectronique Quantique" 2011
Magnetism and Many Body Effects at the Atomic and Molecular Scale Studied with Scanning Probe Methods
Mardi 13 Decembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Markus TERNES (Max-Planck-Institute, Stuttgart, Allemagne) At the interface between classical and quantum mechanical description molecular magnetism has opened novel approaches in information storage, spintronics and quantum computation. In my talk I will present results on probing magnetic structures on thin insulators...
[en savoir plus]Anderson localization in two coupled disordered chains: who wins the fast or the slow?
Mardi 29 Novembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Vladimir KRAVTSOV (International Centre for Theoretical Physics, Trieste, Italie) We solved exactly the problem of Anderson localization on two coupled disordered chains. Contrary to a frequent confusion, this problem does not reduce to solution of DMPK equation which is a simplified version of the Dorokhov approach...
[en savoir plus]Quantum phase-slips in Josephson junction chains : effects of finite size and propagating modes
Mardi 22 Novembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Gianluca RASTELLI (LPMMC, Grenoble) The macroscopic degrees of freedom in superconducting nano-devices realized with one or several Josephson junctions show a quantum behavior when they are cooled at very low temperature and when they are fabricated in electrical circuits opportunely engineered to reduce the...
[en savoir plus]Microwave kinetic inductance detectors (MKIDs) - principles and applications
Mardi 15 Novembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Christian HOFFMANN (Institut Néel, Grenoble) A new type of superconducting detector, the Microwave Kinetic Inductance Detector, has recently drawn the attention of the low-temperature detector community. Easy fabrication, high sensitivity, low time constants and most notably the intrinsic capability to frequency multiplexing open new...
[en savoir plus]Dirac fermions in Hg Te quantum wells
Mardi 8 Novembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Laurens MOLENKAMP (University of Wurzburg, Allemagne) HgTe quantum wells have a linear band dispersion at low energies and thus mimic the Dirac Hamiltonian. Changing the well width tunes the band gap (i.e., the Dirac mass) from positive, through zero, to negative. Wells with a negative Dirac mass are 2-dimensional...
[en savoir plus]Spin Currents and Spin Accumulations in Mesoscopic Systems
Mardi 18 Octobre 2011 à 15h Salle "Rémy Lemaire" K 223 (1er étage) Bat. K, Institut Néel / CNRS Philippe JACQUOD (Université d'Arizona, Etats-Unis) Spintronics refers to spin-based electronics, where information processing and storage are based on the spin, rather than the charge degree of freedom of the electron. This is significantly harder than to control electric charges, but holds great...
[en savoir plus]Strain and nematic phase of electrons in bilayer graphene
Mardi 11 Octobre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Vladimir I FALKO (Lancaster University, Royaume-Uni) Electrons in bilayer graphene exhibit quite unusual properties: they can be viewed as 'massive chiral fermions' with parabolic dispersion at intermediate energies and Berry phase 2π [1, 2], in contrast to monolayer graphene, where electrons are Berry-phase π...
[en savoir plus]The thin film Giaever transformer - vortex drag in a superconductor thin-film bilayer
Mardi 27 Septembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Gil REFAEL (Caltech Institute, Pasadena, Etats-Unis) The normal-field induced superconductor-insulator transition in amorphous thin films, and the possible intervening metallic state, can be qualitatively explained within two paradigms: as vortex condensation, or as a percolation transition between the competing normal and...
[en savoir plus]Anomalous dephasing in electronic Mach-Zehnder interferometers
Mardi 20 Septembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Eugene SUKHORUKOV (Université de Genève, Suisse) Recently, Aharonov-Bohm (AB) effect in electronic Mach-Zehnder (MZ) interferometers has attracted much attention among experimental and theoretical physicists. These interferometers, for the first time experimentally realized in the group of Heiblum, utilize quantum Hall edge states in...
[en savoir plus]Magnetic ordering of localized moments in Dirac conductors
Mardi 13 Septembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Vadim CHEIANOV (Université de Lancaster , royaume-Uni) Localized impurities randomly positioned on the surface of a two-dimensional material supporting excitations with massless Dirac spectrum are shown to exhibit a non-analytic dependence on 1/T at high temperature. This effect is caused by the non-integrable...
[en savoir plus]Identifications of solitons in quasi 1D electronic systems and generalisations to strong correlations in higher dimensions
Mardi 6 Septembre 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Serguei BRAZOVSKII (LPTMS, Orsay) We review a progress in experiments and theory, elucidating the role of microscopic solitons in quasi-1D electronic systems with a symmetry breaking. The recent interest rises from a discovery of the ferroelectric charge ordering in organic conductors, and from nano-scale tunneling...
[en savoir plus]Residual quasiparticles, Andreev current and photon-assisted tunneling in Coulomb blockaded normal-superconductor junctions
Mardi 30 Aout 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Jukka PEKOLA (Low Temperature Laboratory, Aalto University School of Science, Finland) We are developing a precise source of electrical current I=ef, where f is the operation frequency. This device is based on normal metal superconductor (NIS) tunnel junctions. In order to suppress errors in electron transfer,...
[en savoir plus]Fractional Topological Insulators
Mardi 12 Juillet 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Andrei BERNEVIG (Université de Princeton, Etats-Unis) In the past several years tremendous theoretical and experimental effort has been devoted to predicting and observing a new class of materials called topological insulators. These materials are non-interacting band insulators whose Bloch band topology forces...
[en savoir plus]Quantum Optics with Superconducting Circuits: Exploring Propagating Microwave Photons
Mardi 5 Juillet 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Andreas WALRAFF (ETH Zurich, Switzerland) Using modern micro and nano-fabrication techniques combined with superconducting materials we realize quantum electronic circuits. We create, store, and manipulate individual microwave photons on a chip. The strong interaction of photons with superconducting quantum...
[en savoir plus]Entanglement and Fluctuations in Many-Body Quantum Systems
Mardi 28 Juin 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Karyn LE HUR (Université de Yale, Etats-Unis) The study of quantum many-body systems has traditionally involved the analysis of ground state and excited state energies, correlation functions, and symmetry-breaking order parameters to characterize different states of matter. Recently,...
[en savoir plus]Quantum Phase Transition and Emergent Symmetry in Quadruple Quantum Dot System
Mardi 21 Juin 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'Institut Néel/CNRS Harold BARANGER (Duke University, USA & Chaire d'Excellence de la Fondation Nanosciences) I shall discuss a system of four quantum dots designed to study the competition between three types of interactions: Heisenberg, Kondo and Ising. The competition produces a rich phase diagram...
[en savoir plus]Spin Hall effect at interfaces between quantum spin Hall insulators and metals
Mardi 14 Juin 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Marine GUIGOU (Université de Würzburg, Allemagne) The Spin Hall effect (SHE) is a physical phenomenon [Dya71] realized in nonmagnetic systems and that allows for a transverse spin current generated if an electrical charge current is driven in longitudinal direction. This can happen due to...
[en savoir plus]Confinement-Induced Vortex Fusion and Giant Vortex States in Superconductors
Mardi 7 Juin 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Dimitri RODITCHEV (Institut des Nanosciences de Paris) When put in rotation, macroscopic quantum condensates develop a very peculiar collective response: They split in a huge number of small quantum tornados - vortices - that organize in a lattice [1]. The vortex currents circulate owing...
[en savoir plus]Detecting non-abelian quantum Hall state via thermal measurements
Mardi 31 Mai 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Sourin DAS (Université de Delhi, India) I will first discuss recent experimental attempts to detect the non-abelian nature of the nu = 5/2 quantum Hall state. Then I will talk about our theoretical proposal for detection of neutral modes which exist at the boundary of the nu = 5/2 quantum Hall state...
[en savoir plus]Coherent Electron-Phonon Coupling in Tailored Quantum Systems
Mardi 24 Mai 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Preden ROULLEAU (Service de Physique de l'Etat Condense, CEA Saclay et ETH Zurich) The coupling between a two-level system and its environment leads to decoherence. Within the context of coherent manipulation of electronic or quasiparticle states in nanostructures, it is crucial to understand...
[en savoir plus]Scanning tunneling spectroscopy at low temperature: Quantum Hall systems and Graphene
Mardi 17 Mai 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Markus MORGENSTERN (Université de Aachen, Allemagne) Scanning tunneling spectroscopy at low temperature is an invaluable tool to probe systems driven by local inhomogeneities. Two examples will illustrate the strength of the method. Firstly, the transition between localized and critical states of a...
[en savoir plus]Josephson Current Through One Atom
Mardi 10 Mai 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Cristian URBINA (Groupe de quantronique, CEA Saclay) Whatever the nature of a weak-link connecting two superconductors (be it a tunnel junction, a nanowire or a molecule), the Josephson effect can be described in a universal way in terms of “Andreev bound states”. These are localized...
[en savoir plus]The bright side of Coulomb blockade
Mardi 3 Mai 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Fabien PORTIER (Service de Physique de l'Etat Condense, CEA Saclay) The electromagnetic environment of a tunnel junction can modify the current through the junction because the sudden charge transfer associated with a tunnel event can generate photons in the environment. This dissipation process,...
[en savoir plus]Majorana fermions in topological insulators
Mardi 19 Avril 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Carlo BEENAKKER (Université de Leiden, Pays-Bas) Majorana fermions are spatially localized superpositions of electron and hole excitations in the middle of a superconducting energy gap. These unusual particles have been predicted to occur at the interface between a magnetic and superconducting electrode, in contact with a...
[en savoir plus]Equilibration and Transport in 1D quantum wires
Mardi 12 Avril 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Tobias MICKLITZ (Université Libre de Berlin, Allemagne) We study the effect of equilibration on the transport properties of a weakly interacting one-dimensional electron system. Although equilibration in one-dimensional systems is severely suppressed due to phase-space restrictions and conservation laws, it can lead to...
[en savoir plus]Imaging Coulomb islands inside a quatum Hall interferometer
Mardi 29 Mars 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Vincent BAYOT (Université Catholique de Louvain/ Chaire d'Excellence de la Foundation Nanosciences) In the quantum Hall (QH) regime, near integer filling factors, electrons should only be transmitted through spatially separated edge states. However, in mesoscopic systems, electronic...
[en savoir plus]Majorana fermions and the superconductor proximity effect in half-metallic ferromagnets
Mardi 8 Mars 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Piet BROUWER (Université Libre de Berlin) Because of the complete absence of minority carriers in a half metal, Andreev reflection is not possible at the interface between a half metal and an s-wave superconductor, unless the spin-rotation symmetry around the magnetization axis in the half metal is broken. In that...
[en savoir plus]The watt balance route towards a new definition of the kilogram
Mardi 1 Mars 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Ali EICHENBERGER (Office Fédéral de Metrologie METAS) Today, the kilogram is the last unit of the International System of Units (SI) still based on an artefact: the international prototype of the kilogram K which is kept at the Bureau International des Poids et Mesure (BIPM). The international comparisons...
[en savoir plus]Preparation and measurement of multi-qubit entanglement
Mardi 22 Février 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Leonardo DICARLO (Université de Technologie de Delft, Pays-Bas) Entanglement has traditionally played a central role in foundational discussions of quantum mechanics. Correlation measurements between entangled quantum particles exhibit results at odds with classical...
[en savoir plus]Using a Josephson junction for manipulating microscopic atomic dipoles
Mardi 15 Février 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Alexey USTINOV (Université de Karlsruhe, Allemagne) Experiments with quantized Josephson plasma oscillations in tunnel junctions display signatures of coherent coupling to individual microscopic defects acting as two-level systems (TLSs). These defects manifest...
[en savoir plus]Periodic Nanowire Structures
Mardi 08 Février 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Erik BAKKERS (Université de Technologie de Eindhoven et Université de Technologie de Delf, Pays Bas) Semiconducting nanowires offer the possibility of nearly unlimited complex bottom-up design on intrawire and interwire level, which allows for new (opto-)electronic device concepts, such as single-photon...
[en savoir plus]How to measure tunnelling charges without recourse to current noise?
Mardi 1 Février 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Inès SAFI (Laboratoire de Physique des Solides, Orsay) In low dimensional conductors, electronic correlations can give rise to quasi-particles carrying an electric charge q different from the elementary electron charge e. This is for instance the case for...
[en savoir plus]Localization of preformed Cooper pairs in highly disordered superconducting films
Mardi 25 Janvier 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Claude CHAPELIER (CEA-INAC/SPSMS/LATEQS) I will present a study combining tunnelling spectroscopy and point-contact Andreev spectroscopy on disordered superconducting indium oxide films. These samples are in the vicinity of the metal-insulator Anderson transition. Tunneling spectroscopy highlights a rather unusual superconducting...
[en savoir plus]Quantum glasses – frustration and collective behavior at zero temperature
Mardi 18 Janvier 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Markus MÜLLER (ICTP Trieste) Glasses are strongly interacting and disordered systems, which develop rather unusual amorphous order at low temperatures. The phase transition into the glass state is marked by the loss of ergodicity, i.e., the localization in phase space due to the emergence of high energy barriers. A...
[en savoir plus]Nanotechnology with graphene, nanotubes and diamond-like carbon
Mardi 11 Janvier 2011 à 15h00 Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS Andrea FERRARI (Department of Engineering, University of Cambridge) Carbon based materials play a major role in today's science and technology. Carbon is a very versatile element, which can crystallise in the form of diamond or graphite. Great excitement has followed the discovery of new forms of carbon,...
[en savoir plus]