Catégorie : Collaborations

Auteurs

N. Kirova 1 S. Brazovski 2 A. Choi 3 Y. W. Park 3
1 LPS – Laboratoire de Physique des Solides
2 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
3 Department of Physics and Astronomy [Seoul]

Abstract : Polymer nanofibers are one-dimensional organic hydrocarbon systems containing conducting polymers where the non-linear local excitations such as solitons, polarons and bipolarons formed by the electron-phonon interaction were predicted. Magnetoconductance (MC) can simultaneously probe both the spin and charge of these mobile species and identify the effects of electron-electron interactions on these nonlinear excitations. Here we report our observations of a qualitatively different MC in polyacetylene (PA) and in polyaniline (PANI) and polythiophene (PT) nanofibers. In PA the MC is essentially zero, but it is present in PANI and PT. The universal scaling behavior and the zero (finite) MC in PA (PANI and PT) nanofibers provide evidence of Coulomb interactions between spinless charged solitons (interacting polarons which carry both spin and charge).

Auteurs

A. Choi 1, 2 K. H. Kim 1 S. J. Hong 1 M. Goh 3, 4 K. Akagi 3 R. B. Kaner 5 N. N. Kirova 6 S. A. Brazovskii 7 A. T. Johnson 8, 9 D. A. Bonnell 8 E. J. Mele 9 Y. W. Park 1
1 Department of Physics and Astronomy [Seoul]
2 WCU Flexible Nanosystems
3 Department of Polymer Chemistry
4 Institute of Advanced Composite Materials
5 Department of Chemistry and Biochemistry
6 LPS – Laboratoire de Physique des Solides
7 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
8 Nano-Bio Interface Center
9 Department of Physics and Astronomy [Philadelphia]

Yohann Benard 1 Norberto Lopez-Gil Richard Legras 2
1 LAC – Laboratoire Aimé Cotton
2 LuMIn – Laboratoire Lumière, Matière et Interfaces

Abstract : We study Johnson-Nyquist noise in macroscopically inhomogeneous disordered metals and give a microscopic derivation of the correlation function of the scalar electric potentials in real space. Starting from the interacting Hamiltonian for electrons in a metal and the random phase approximation, we find a relation between the correlation function of the electric potentials and the density fluctuations which is valid for arbitrary geometry and dimensionality. We show that the potential fluctuations are proportional to the solution of the diffusion equation, taken at zero frequency. As an example, we consider networks of quasi-1D disordered wires and give an explicit expression for the correlation function in a ring attached via arms to absorbing leads. We use this result in order to develop a theory of dephasing by electronic noise in multiply-connected systems.

M. Treiber 1 C. Texier 2, 3 O. M. Yevtushenko 1 J. von Delft 1 I. V. Lerner 4
1 Arnold Sommerfeld Center and Center for Nano-Science
2 LPS – Laboratoire de Physique des Solides
3 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
4 School of Physics and Astronomy

Abstract : We consider the Schroedinger equation with a supersymmetric random potential, where the superpotential is a Levy noise. We focus on the problem of computing the so-called complex Lyapunov exponent, whose real and imaginary parts are, respectively, the Lyapunov exponent and the integrated density of states of the system. In the case where the Levy process is non-decreasing, we show that the calculation of the complex Lyapunov exponent reduces to a Stieltjes moment problem, we ascertain the low-energy behaviour of the density of states in some generality, and relate it to the distributional properties of the Levy process. We review the known solvable cases, where the complex Lyapunov exponent can be expressed in terms of special functions, and discover a new one.

Alain Comtet 1, 2 Christophe Texier 2, 3 Yves Tourigny 4
1 IHP – Institut Henri Poincaré
2 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
3 LPS – Laboratoire de Physique des Solides
4 School of Mathematics [Bristol]

Abstract : One dimensional free-fermions and hard-core bosons are often considered to be equivalent. Indeed, when restricted to nearest-neighbor hopping on a chain the particles cannot exchange themselves, and therefore hardly experience their own statistics. Apart from the off-diagonal correlations which depends on the so-called Jordan-Wigner string, real-space observables are similar for free-fermions and hard-core bosons on a chain. Interestingly, by coupling only two chains, thus forming a two-leg ladder, particle exchange becomes allowed, and leads to a totally different physics between free-fermions and hard-core bosons. Using a combination of analytical (strong coupling, field theory, renormalization group) and numerical (quantum Monte Carlo, density-matrix renormalization group) approaches, we study the apparently simple but non-trivial model of hard-core bosons hopping in a two-leg ladder geometry. At half-filling, while a band insulator appears for fermions at large interchain hopping tperp >2t only, a Mott gap opens up for bosons as soon as tperp\neq0 through a Kosterlitz-Thouless transition. Away from half-filling, the situation is even more interesting since a gapless Luttinger liquid mode emerges in the symmetric sector with a non-trivial filling-dependent Luttinger parameter 1/2\leq Ks \leq 1. Consequences for experiments in cold atoms, spin ladders in a magnetic field, as well as disorder effects are discussed. In particular, a quantum phase transition is expected at finite disorder strength between a 1D superfluid and an insulating Bose glass phase.

François Crépin 1 Nicolas Laflorencie 1 Guillaume Roux 2 Pascal Simon 1
1 LPS – Laboratoire de Physique des Solides
2 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques

Abstract : We develop a method to predict the existence of edge states in graphene ribbons for a large class of boundaries. This approach is based on the bulk-edge correspondence between the quantized value of the Zak phase Z(k), which is a Berry phase across an appropriately chosen one-dimensional Brillouin zone, and the existence of a localized state of momentum k at the boundary of the ribbon. This bulk-edge correspondence is rigorously demonstrated for a one dimensional toy model as well as for graphene ribbons with zigzag edges. The range of k for which edge states exist in a graphene ribbon is then calculated for arbitrary orientations of the edges. Finally, we show that the introduction of an anisotropy leads to a topological transition in terms of the Zak phase, which modifies the localization properties at the edges. Our approach gives a new geometrical understanding of edge states, it con?firms and generalizes the results of several previous works.

Auteurs

P. Delplace 1 D. Ullmo 2 G. Montambaux 3
1 Département de Physique
2 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
3 LPS – Laboratoire de Physique des Solides

Abstract : We study a generalized Thomson problem that appears in several condensed matter settings: identical point-charge particles can penetrate inside a homogeneously charged sphere, with global electro-neutrality. The emphasis is on scaling laws at large Coulombic couplings, and deviations from mean-field behaviour, by a combination of Monte Carlo simulations and an analytical treatment within a quasi-localized charge approximation, which provides reliable predictions. We also uncover a local overcharging phenomenon driven by ionic correlations alone.

Auteurs

A. D. Chepelianskii 1 F. Closa 2 E. Raphael 2 E. Trizac 3
1 LPS – Laboratoire de Physique des Solides
2 Gulliver (UMR 7083)
3 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques

Abstract : We investigate theoretically an original route to achieve Bose-Einstein condensation using dark power-law laser traps. We propose to create such traps with two crossing blue-detuned Laguerre-Gaussian optical beams. Controlling their azimuthal order ℓℓ allows for the exploration of a multitude of power-law trapping situations in one, two and three dimensions, ranging from the usual harmonic trap to an almost square-well potential, in which a quasi-homogeneous Bose gas can be formed. The usual cigar-shaped and disk-shaped Bose-Einstein condensates obtained in a 1D or 2D harmonic trap take the generic form of a « finger » or of a « hockey puck » in such Laguerre-Gaussian traps. In addition, for a fixed atom number, higher transition temperatures are obtained in such configurations when compared with a harmonic trap of same volume. This effect, which results in a substantial acceleration of the condensation dynamics, requires a better but still reasonable focusing of the Laguerre-Gaussian beams.

Amine Jaouadi 1, 2 Naceur Gaaloul 3 Bruno Viaris de Lesegno 4 Mourad Telmini 1 Laurence Pruvost 4 Eric Charron 5, *
* Auteur correspondant
1 LSAMA – Laboratoire de Spectroscopie Atomique, Moléculaire et Applications
2 ISMO – Institut des Sciences Moléculaires d’Orsay
3 IQ – Institut für Quantenoptik [Hannover]
4 LAC – Laboratoire Aimé Cotton
5 Approches théoriques en dynamique quantique
ISMO – Institut des Sciences Moléculaires d’Orsay

Hélène Rouger 1 Yohann Benard Richard Legras 2
1 LAC – Laboratoire Aimé Cotton
2 LuMIn – Laboratoire Lumière, Matière et Interfaces