Conformational Control of Exciton-Polariton Physics in Metal - Poly(9,9-dioctylfluorene) - Metal Cavities

Control is exerted over the exciton-polariton physics in metal - Poly(9,9-dioctyl fluorene) - metal microcavities via conformational changes to the polymer backbone. Using thin-film samples containing increasing fractions of $\beta$-phase chain segments, a systematic study is reported for the mode characteristics and resulting light emission properties of cavities containing two distinct exciton sub-populations within the same semiconductor. Ultrastrong coupling for disordered glassy-phase excitons is observed from angle-resolved reflectivity measurements, with Rabi splitting energies in excess of 1.05 eV (more than 30% of the exciton transition energy) for both TE- and TM-polarized light. A splitting of the lower polariton branch is then induced via introduction of $\beta$-phase excitons and increases with their growing fraction. In all cases, the photoluminescence emanates from the lowermost polariton branch, allowing conformational control to be exerted over the emission energy and its angular variation. Dispersion-free cavities with highly saturated blue-violet emission are thus enabled. Experimental results are discussed in terms of the full Hopfield Hamiltonian generalized to the case of two exciton oscillators. The importance of taking account of the molecular characteristics of the semiconductor for an accurate description of its strong coupling behaviour is directly considered, in specific relation to the role of the vibronic structure

Dynamical behavior of a complex fluid near an out-of-equilibrium transition: approaching simple rheological chaos

We report here an extensive study of sustained oscillations of the viscosity of a complex fluid near an out-of-equilibrium transition. Using well defined protocols, we perform rheological measurements of the onion texture near a layering transition in a Couette flow. This complex fluid exhibits sustained oscillations of the viscosity, on a large time scale (500s) at controlled stress. These oscillations are directly correlated to an oscillating microstrutural change of the texture of the fluid. We observe a great diversity of dynamical behavior and we show that there is a coupling with spatial effects in the gradient v direction. This is in agreement with a carefull analysis of the temporal series of the viscosity with the dynamical system theory. This analysis indicates that the observed dynamical responses do not strictly correspond to 3-dimensional chaotic states, probably because some spatio-temporal effects are present and are likely to play an important role.Comment: submitted to Phys. Rev.

On quantization of quadratic Poisson structures

Any classical r-matrix on the Lie algebra of linear operators on a real vector space V gives rise to a quadratic Poisson structure on V which admits a deformation quantization stemming from the construction of V. Drinfel'd. We exhibit in this article an example of quadratic Poisson structure which does not arise this way.Comment: Submitted to Comm. Math. Phys. Version 2 : error in introduction correcte

Breakdown patterns in Branly's coheror

We use thermal imaging of Joule heating to see for the first time electrical conducting paths created by the so-called Branly effect in a two-dimensional metallic granular medium (aluminium). Multiple breakdowns are shown to occur when the medium is submitted to high voltage increases (more than 500 V) with rise times close to one hundred of microseconds.Comment: 4 pages, 5 figures, related informations at http://chemphys.weizmann.ac.il/~damien/index.htm

Bosonization and density-matrix renormalization group studies of Fulde-Ferrell-Larkin-Ovchinnikov phase and irrational magnetization plateaus in coupled chains

We review the properties of two coupled fermionic chains, or ladders, under a magnetic field parallel to the lattice plane. Results are computed by complementary analytical (bosonization) and numerical (density-matrix renormalization group) methods which allows a systematic comparison. Limiting cases such as coupled bands and coupled chains regimes are discussed. We particularly focus on the evolution of the superconducting correlations under increasing field and on the presence of irrational magnetization plateaus. We found the existence of large doping-dependent magnetization plateaus in the weakly-interacting and strong-coupling limits and in the non-trivial case of isotropic couplings. We report on the existence of extended Fulde-Ferrell-Larkin-Ovchinnikov phases within the isotropic t-J and Hubbard models, deduced from the evolution of different observables under magnetic field. Emphasis is put on the variety of superconducting order parameters present at high magnetic field. We have also computed the evolution of the Luttinger exponent corresponding to the ungaped spin mode appearing at finite magnetization. In the coupled chain regime, the possibility of having polarized triplet pairing under high field is predicted by bosonization.Comment: 18 pages, 19 figure

Scattering by a toroidal coil

In this paper we consider the Schr\"odinger operator in ${\mathbb R}^3$ with a long-range magnetic potential associated to a magnetic field supported inside a torus ${\mathbb{T}}$. Using the scheme of smooth perturbations we construct stationary modified wave operators and the corresponding scattering matrix $S(\lambda)$. We prove that the essential spectrum of $S(\lambda)$ is an interval of the unit circle depending only on the magnetic flux $\phi$ across the section of $\mathbb{T}$. Additionally we show that, in contrast to the Aharonov-Bohm potential in ${\mathbb{R}}^2$, the total scattering cross-section is always finite. We also conjecture that the case treated here is a typical example in dimension 3.Comment: LaTeX2e 17 pages, 1 figur