Search query: Spontaneous Bose Coherence of Excitons and Polaritons

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abstract: In the past decade, there has been an increasing number of experiments on spontaneous Bose coherence of excitons and polaritons. Four major areas of research are reviewed here: three dimensional excitons in the bulk semiconductor Cu2O, two dimensional excitons in coupled quantum wells, Coulomb drag experiments in coupled two dimensional electron gases, and polaritons in semiconductor microcavities. The unifying theory of all these experiments is the effect of spontaneous symmetry breaking in the Bose Einstein condensation phase transition.
author_names: David W Snoke
title: Spontaneous Bose Coherence of Excitons and Polaritons
venue: Science
year: 2002

abstract: Electrons, holes, and photons in semiconductors are interacting fermions and bosons. In this system, a variety of ordered coherent phases can be formed through the spontaneous phase symmetry breaking because of their interactions. The Bose Einstein condensation (BEC) of excitons and polaritons is one of such coherent phases, which can potentially crossover into the Bardeen Cooper Schrieffer (BCS) type ordered phase at high densities under quasi equilibrium conditions, known as the BCS BEC crossover. In contrast, one can find the semiconductor laser, superfluorescence (SF) and superradiance as relevant phenomena under nonequilibrium conditions. In this paper, we present a comprehensive generating functional theory that yields nonequilibrium Green's functions in a rigorous way. The theory gives us a starting point to discuss these phases in a unified view with a diagrammatic technique. Comprehensible time dependent equations are derived within the Hartree Fock approximation, which generalize the Maxwell Semiconductor Bloch equations under the relaxation time approximation. With the help of this formalism, we clarify the relationship among these cooperative phenomena and we show theoretically that the Fermi edge SF is directly connected to the e h BCS phase. We also discuss the emission spectra as well as the gain absorption spectra.
author_names: Makoto Yamaguchi

Ryota Nii

Kenji Kamide

Tetsuo Ogawa

Yoshihisa Yamamoto
title: Generating functional approach for spontaneous coherence in semiconductor electron hole photon systems
year: 2015

abstract: Abstract Quasi two dimensional (2D) exciton polaritons in single and coupled quantum wells or quantum dots embedded in an optical microcavity in magnetic field are considered. The dependencies of exciton properties on control parameters are obtained. Magnetic field influence on polariton resonance, splitting and dispersion is studied. Effects of spontaneous coherence and Kosterlitz Thouless transition and Bose Einstein condensation for such systems are discussed.
author_names: Natalia E Kaputkina

Yurii E Lozovik
title: Indirect excitons in coupled quantum dots and exciton polaritons in optical microcavities in magnetic field
year: 2008

abstract: Influence of external magnetic field and confinement on direct and spatially indirect excitons is studied. Exciton photon interaction and exciton polariton formation are discussed for single and coupled quantum wells or quantum dots embedded in optical microcavity. Possibility to control polariton resonance, polariton splitting and polariton dispersion by magnetic field is studied analitically and numerically. Magnetic field changes effective mass of magnetoexciton. Magneticfield increases effective steepness of confining potential in quantum dots also. This leads to the transformation of exciton energy spectrum. At low temperatures spontaneous coherence and Kosterlitz Thouless transition to superfluid state of exciton polaritons in the system of coupled quantum wells embedded in microcavity or Bose Einstein condensation of exciton polaritons in the system of coupled quantum dots embedded in optical microcavity can take place. (c) 2009 WILEY VCH Verlag GmbH Co. KGaA, Weinheim)
author_names: Natalia E Kaputkina

Yurii E Lozovik
title: Influence of external magnetic field and confinement on spectrum rearrangement and exciton polaritons in optical microcavity
year: 2009

abstract: In this thesis, we study two different aspects of many particle physics. In the first part, we study the Bose Einstein condensation of microcavity exciton polaritons in different artificial lattices. Bose Einstein condensation is a quantum phase transition, which allows the system to macroscopically occupy its ground state and develop coherence spontaneously. Often studied in microcavities, which are optical cavities that trap light at specific wavelengths, exciton polaritons are a kind of quasiparticle arising from the strong coupling between quantum well excitons and cavity photons. By periodically aligning cavity pillars in different patterns, one can achieve different artificial lattice structures. With this setup, we apply the driven dissipative Gross Pitaevskii equations to investigate the different consequences of the condensation by changing the pumping schemes and the design of the trapping potentials. Topics include multivalley condensation, phase selection and intermittency of exciton polariton condensation, flat band condensation, and exciton polariton topological insulators. In the second part of this thesis, we focus on the electron scattering properties of a hybrid Bose Fermi system. We consider a system consisting of a spatially separated two dimensional electron gas layer and an exciton gas layer that interacts via Coulomb forces. We study the temperature dependence of the system's resistivity with this interlayer electron exciton interaction and compare the results with the electron phonon interaction.
author_names: Meng Sun
title: Exciton Polaritons in Artificial Lattices and Electron Transport in Bose Fermi Hybrid Systems.
year: 2020

abstract: Spontaneous coherence and Kosterlitz Thouless transition to superfluid state of exciton polaritons in the system of coupled quantum wells embedded in microcavity was considered at low temperatures. Contrary to the infinite two dimensional system without confinement, the Bose Einstein condensation of exciton polaritons in the system of coupled quantum dots embedded in optical microcavity can take place. Growth of confining potential steepness fleads to the increase of the critical temperature. Magnetic field influence on the critical temperature can be non monotonous for certain region of control parameters because of the competition of two mechanisms: (i) growth of the effective mass of magnetoexciton which leads to decreasing of critical temperature; and (ii) growth of effective parameter of confinement, which increases the critical temperature and favors condensate formation.
author_names: Natalia E Kaputkina

Yurii E Lozovik
title: Effects of magnetic field and confining potential on spontaneous coherence of exciton polaritons in coupled quantum wells and dots embedded in optical microcavity
year: 2012

abstract: Microcavity exciton polaritons are the eigenstates resulting from strong light matter coupling in high quality monolithic semiconductor microcavities. Owing to their mixed photonic and excitonic nature, polaritons are Bose particles of very light mass and short lifetime that can interact with their environment, forming a new class of Bose gas. In spite of their short lifetime, a polariton gas can show Bose Einstein condensation or polariton lasing depending on the experimental conditions. The properties of these coherent states of polaritons are unique in many respects. In this chapter we rely on a comprehensive set of experimental and theoretical works carried out this last decade to give a detailed description of polariton coherent states. The influences of finite lifetime, disorder and interaction with the environment are addressed, and the analogies and differences between polariton condensate, polariton lasing, equilibrium Bose gas and photon lasing are outlined and discussed.
author_names: Maxime Richard

Michiel Wouters

Le Si Dang
title: Spontaneous coherence within a gas of exciton polaritons in Telluride microcavities
year: 2010

abstract: The spontaneous breaking of the continuous symmetries of a two dimensional electron hole system in a strong magnetic field perpendicular to the plane leads to the formation of new ground states and determines the energy spectrum of collective elementary excitations that appear above these new ground states. In this review, the main attention is paid to the electron hole system formed from coplanar magnetoexcitons under conditions of Bose Einstein condensation in the ground state with the wave vector k 0 taking into account the influence of excited Landau levels, when exciton type elementary excitations coexist with plasmon type oscillations. At the same time, the properties of a two component system consisting of a two dimensional electron gas and a two dimensional hole gas spatially separated in a double quantum well under conditions of the fractional quantum Hall effect are of great interest, because these properties can affect the quantum states of magnetic excitons that are formed when the distance between the layers tends to zero. Bilayer electron systems are also considered under conditions of the fractional quantum Hall effect with the one half filling factor for each layer and the total filling factor equal to unity for both layers. The coherence between the electron states in the two layers is equivalent to the formation of excitons in a macroscopic coherent state. This makes it possible to compare the energy spectrum of collective elementary excitations of Bose Einstein condensed excitons under conditions of the quantum Hall effect and coplanar magnetoexcitons. The breaking of the global gauge symmetry or of the continuous rotational symmetry leads to the formation of a gapless spectrum of the Nambu Goldstone type, whereas the breaking of the local gauge symmetry is accompanied by the appearance of a gap in the energy spectrum (Higgs phenomenon) These phenomena are equivalent to the formation of massless and massive particles in the relativistic physics. The application of the Nielsen Chadha theorem, which determines the number of Nambu Goldstone modes as a function of the number of broken symmetry operators, is demonstrated using the example of Bose Einstein condensation of spinor atomic gases in an optical trap. This example is presented for a better understanding of the results obtained in the case of a Bose Einstein condensation of coplanar magnetoexcitons. The Higgs phenomenon leads to the formation of composite particles under conditions of the fractional quantum Hall effect. Their description is given in terms of the Ginzburg Landau theory. The possibilities for the appearance of spontaneous coherence in a system of indirect excitons in structures with a double quantum well are analyzed. The experimental attempts to create these conditions, the main results obtained in this field, and the accumulated knowledge are reviewed. The basic properties of the energy spectrum of magnetoexciton polaritons in a microcavity are formulated. A hypothesis is put forward about the possibility of forming two dimensional magnetoexcitons and two dimensional magnetoexciton polaritons of high density with attached point quantum vortices, i.e. about the possibility of forming new composite particles.
author_names: S A Moskalenko

Michael A Liberman

E S Moskalenko

E V Dumanov

Ig V Podlesny
title: Coherence of two dimensional electron hole systems: Spontaneous breaking of continuous symmetries: A review
year: 2013

abstract: Over the last two decades, the system of exciton polaritons (polaritons) in a semiconductor microcavity has become an important platform for studying the physics of quantum fluids in a solid state system. Polaritons are formed by the strong coupling between photons and a sharp electronic resonance (e.g. an exciton resonance) in a cavity. They are interacting bosonic particles with a small effective mass due to their half light and half matter nature. Spontaneous coherence phenomena, such as the superfluid transition and Bose Einstein condensation (BEC) have been observed in polariton systems at temperatures in the range from several Kelvin to room temperature. This dissertation focuses on new methods of trapping polaritons and the BEC and superfluidity of polaritons in these new traps. The first part of this dissertation describes experiments on trapping polaritons with an optically generated potential barrier. When the polariton density increases, there is a transition from ballistic motion to coherent motion of polaritons over hundreds of micrometers. At even higher particle density, there is a very sharp transition from the coherent motion state to the ground state of the trap. The second part of this dissertation explores the superfluid properties of polaritons in a ring shaped trap. This ring trap is formed by combining a stress induced harmonic trap with an optically created barrier at the trap center. This trapping method enables fine control of the trap profile as well as the properties of the polaritons in the trap. The formation of a polariton ring condensate is observed in this trap. The phase and polarization measurement of the ring condensate reveals that it is in a half quantized circulation state which features a phase shift of p and a polarization vector rotation of p of the polaritons around a closed path in the ring. The direction of the circulation of the flow around the ring fluctuates randomly between clockwise and counter clockwise from one shot to the next. In contrast, the rotation of the polarization of polaritons is very stable. This property is experimentally studied, and it is found that the stable spatial polarization pattern may relate to the optical spin Hall effect.
author_names: Gangqiang Liu
title: Bose Einstein condensation and quantized flow of microcavity polaritons with long lifetime
year: 2015

abstract: Bose Einstein condensate of exciton polaritons in a semiconductor microcavity is a macroscopically populated coherent quantum state subject to concurrent pumping and decay. Debates about the fundamental nature of the condensed phase in this open quantum system still persist. Here, we gain a new insight into the spontaneous condensation process by imaging long lifetime exciton polaritons in a high quality inorganic microcavity in the single shot optical excitation regime, without averaging over multiple condensate realisations. In this highly non stationary regime, a condensate is strongly influenced by the `hot' incoherent reservoir, and reservoir depletion is critical for the transition to the ground energy and momentum state. Condensates formed by more photonic exciton polaritons exhibit dramatic reservoir induced density filamentation and shot to shot fluctuations. In contrast, condensates of more excitonic quasiparticles display smooth density and are second order coherent. Our observations show that the single shot measurements offer a unique opportunity to study formation of macroscopic phase coherence during a quantum phase transition in a solid state system.
author_names: E Estrecho

T Gao

Nataliya Bobrovska

Michael D Fraser

Mark Steger

Loren N Pfeiffer

Ken W West

Timothy C H Liew

Michal Matuszewski

David W Snoke

Andrew G Truscott

Elena A Ostrovskaya
title: Spontaneous condensation of exciton polaritons in the single shot regime
year: 2017