Mediterranean Institute of Fundamental Physics

Rome, Italy

Mediterranean Institute of Fundamental Physics

Rome, Italy

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Matuszewski M.,Instytut Fizyki Polskiej Akademii Nauk | Liew T.C.H.,National Autonomous University of Mexico | Liew T.C.H.,Mediterranean Institute of Fundamental Physics | Rubo Y.G.,National Autonomous University of Mexico | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We calculate the spatial structure of four-component spinor systems of mixed bright and dark exciton condensates in coupled quantum wells. The spin-dependent bright-dark exciton conversion and Dresselhaus spin-orbit coupling is found to generate a rich variety of topological elements. By propagating the Gross-Pitaevskii equation in imaginary time, we observe the following: single and multiple polarized vortices; the phase separation of bright and dark excitons; and exotic spatial structures in density and spin polarization. ©2012 American Physical Society.


High A.A.,University of California at San Diego | Hammack A.T.,University of California at San Diego | Leonard J.R.,University of California at San Diego | Yang S.,University of California at San Diego | And 9 more authors.
Physical Review Letters | Year: 2013

We report the observation of spin currents in a coherent gas of indirect excitons. The realized long-range spin currents originate from the formation of a coherent gas of bosonic pairs - a new mechanism to suppress the spin relaxation. The spin currents result in the appearance of a variety of polarization patterns, including helical patterns, four-leaf patterns, spiral patterns, bell patterns, and periodic patterns. We demonstrate control of the spin currents by a magnetic field. We also present a theory of coherent exciton spin transport that describes the observed exciton polarization patterns and indicates the trajectories of the spin currents. © 2013 American Physical Society.


Kavokin A.V.,CNRS Charles Coulomb Laboratory | Kavokin A.V.,University of Southampton | Vladimirova M.,CNRS Charles Coulomb Laboratory | Jouault B.,CNRS Charles Coulomb Laboratory | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Traditional spintronics relies on spin transport by charge carriers, such as electrons in semiconductor crystals. The challenges for the realization of long-range electron spin transport include rapid spin relaxation due to electron scattering. Scattering and, in turn, spin relaxation can be effectively suppressed in excitonic devices where the spin currents are carried by electrically neutral bosonic quasiparticles: excitons or exciton-polaritons. They can form coherent quantum liquids that carry spins over macroscopic distances. The price to pay is a finite lifetime of the bosonic spin carriers. We present the theory of exciton ballistic spin transport which may be applied to a range of systems supporting bosonic spin transport, in particular to indirect excitons in coupled quantum wells. We describe the effect of spin-orbit interaction for the electron and the hole on the exciton spin, account for the Zeeman effect induced by external magnetic fields and long-range and short-range exchange splittings of the exciton resonances. We also consider exciton transport in the nonlinear regime and discuss the definitions of the exciton spin current, polarization current, and spin conductivity. © 2013 American Physical Society.


Ohadi H.,University of Southampton | Kammann E.,University of Southampton | Liew T.C.H.,Mediterranean Institute of Fundamental Physics | Lagoudakis K.G.,Stanford University | And 3 more authors.
Physical Review Letters | Year: 2012

We report on the simultaneous observation of spontaneous symmetry breaking and long-range spatial coherence both in the strong- and the weak-coupling regime in a semiconductor microcavity. Under pulsed excitation, the formation of a stochastic order parameter is observed in polariton and photon lasing regimes. Single-shot measurements of the Stokes vector of the emission exhibit the buildup of stochastic polarization. Below threshold, the polarization noise does not exceed 10%, while above threshold we observe a total polarization of up to 50% after each excitation pulse, while the polarization averaged over the ensemble of pulses remains nearly zero. In both polariton and photon lasing regimes, the stochastic polarization buildup is accompanied by the buildup of spatial coherence. We find that the Landau criterion of spontaneous symmetry breaking and Penrose-Onsager criterion of long-range order for Bose-Einstein condensation are met in both polariton and photon lasing regimes. © 2012 American Physical Society.


Rumyantsev V.,Galkin Institute for Physics AndEngineering | Rumyantsev V.,Mediterranean Institute of Fundamental Physics | Fedorov S.,Galkin Institute for Physics AndEngineering | Gumennyk K.,Galkin Institute for Physics AndEngineering | And 3 more authors.
Scientific Reports | Year: 2014

We study localized photonic excitations in a quasi-two-dimensional non-ideal binary microcavity lattice with use of the virtual crystal approximation. The effect of point defects (vacancies) on the excitation spectrum is investigated by numerical modelling. We obtain the dispersion and the energy gap of the electromagnetic excitations which may be considered as Frenkel exciton-like quasiparticles and analyze the dependence of their density of states on the defect concentrations in a microcavity supercrystal.


Savenko I.G.,University of Iceland | Savenko I.G.,Nanyang Technological University | Liew T.C.H.,Nanyang Technological University | Liew T.C.H.,Mediterranean Institute of Fundamental Physics | And 2 more authors.
Physical Review Letters | Year: 2013

We present a theory for the description of energy relaxation in a nonequilibrium condensate of bosonic particles. The approach is based on coupling to a thermal bath of other particles (e.g., phonons in a crystal, or noncondensed atoms in a cold atom system), which are treated with a Monte Carlo type approach. Together with a full account of particle-particle interactions, dynamic driving, and particle loss, this offers a complete description of recent experiments in which Bose-Einstein condensates are seen to relax their energy as they propagate in real space and time. As an example, we apply the theory to the solid-state system of microcavity exciton polaritons, in which nonequilibrium effects are particularly prominent. © 2013 American Physical Society.


Manni F.,Ecole Polytechnique Federale de Lausanne | Manni F.,Stanford University | Lagoudakis K.G.,Ecole Polytechnique Federale de Lausanne | Liew T.C.H.,Mediterranean Institute of Fundamental Physics | And 4 more authors.
Nature Communications | Year: 2012

The quest for identification and understanding of fractional vorticity is a major subject of research in the quantum fluids domain, ranging from superconductors, superfluid Helium-3 to cold atoms. In a two-dimensional Bose degenerate gas with a spin degree of freedom, the fundamental topological excitations are fractional vortical entities, called half-quantum vortices. Convincing evidence for the existence of half-quantum vortices was recently provided in spinor polariton condensates. The half-quantum vortices can be regarded as the fundamental structural components of singly charged vortices but, so far, no experimental evidence of this relation has been provided. Here we report on the direct and time-resolved observation of the dynamical process of the dissociation of a singly charged vortex into its primary components, a pair of half-quantum vortices. The physical origin of the observed phenomenology is found in a spatially inhomogeneous static potential that couples the two spin components of the condensate. © 2012 Macmillan Publishers Limited. All rights reserved.


Wertz E.,CNRS Laboratory for Photonics and Nanostructures | Amo A.,CNRS Laboratory for Photonics and Nanostructures | Solnyshkov D.D.,CNRS Pascal Institute | Ferrier L.,CNRS Laboratory for Photonics and Nanostructures | And 10 more authors.
Physical Review Letters | Year: 2012

The dynamics of propagating polariton condensates in one-dimensional microcavities is investigated through time resolved experiments. We find a strong increase in the condensate intensity when it travels through the nonresonantly excited area. This amplification is shown to come from bosonic stimulated relaxation of reservoir excitons into the polariton condensate, allowing for the repopulation of the condensate through nonresonant pumping. Thus, we experimentally demonstrate a polariton amplifier with a large band width, opening the way towards the transport of polaritons with high densities over macroscopic distances. © 2012 American Physical Society.


Liew T.C.H.,Mediterranean Institute of Fundamental Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

A concept of complex reflectivity modulation is proposed based on the electrical control of quantum well exciton resonances that influence the propagation of light in a layered semiconductor structure. By variation in exciton energies, both the intensity and the phase of reflected light can be fully controlled. Unlike previous devices, for full complex light modulation, the design is based on a single device in a single structure. The device allows complete 100% intensity contrast and allows for the construction of small pixel sizes with fast response times. © 2012 American Physical Society.


Chikina I.,CEA Saclay Nuclear Research Center | Shikin V.,Russian Academy of Sciences | Varlamov A.A.,CNR Institute of Neuroscience | Varlamov A.A.,Mediterranean Institute of Fundamental Physics
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

We study Seebeck effect in liquid electrolytes, starting from its simple neutral analog-thermodiffusion (so-called Ludwig-Soret or Soret effect). It is observed that when two or more subsystems of mobile particles are subjected to the temperature gradient, various types of them respond to it differently. In the case when these fractions, with different mobility parameters (Soret coefficients), are oppositely charged (a case typical for electrolytes), the nonhomogeneous internal electric field is generated. The latter field prevents these fractions from space separation and determines the intensity of the appearing Seebeck effect. © 2012 American Physical Society.

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