Despite their name polariton lasers do not rely on stimulated emission of cavity photons. The less stringent threshold conditions are the cause that bosonic polariton lasers can outperform standard lasers in terms of their threshold currents. The part-light and part-matter quasiparticles called polaritons, can undergo a condensation process into a common energy state. The radiated light from such a system shares many similarities with the light emitted from a conventional photon laser, even though the decay of the polaritons out of the finite lifetime cavity is a spontaneous process. We discuss properties of polariton condensates in GaAs based microcavities. The system’s response to an external magnetic field is used as a reliable tool to distinguish between polariton laser and conventional photon laser. In particular, we will discuss the realization of an electrically pumped polariton laser, which manifests a major step towards the exploitation of polaritonic devices in the real world.
Polariton Lasers do not rely on stimulated emission of photons, a criterion that sets stringent conditions on the threshold current in a conventional laser. Therefore, they have the capability to outperform photon lasers in the weak coupling regime in terms of the threshold power consumption. We present the first successful realization of an electrically pumped polariton laser based on a GaAs/AlAs distributed Bragg reflector cavity. We have furthermore identified the system’s response to an applied magnetic field as a sensitive tool to distinguish a polariton laser from a standard VCSEL device in the weak light-matter coupling regime
We study the system with dipolaritons - mixed quasiparticles which are formed in the double quantum well
heterostructure in the presence of strong light-matter interaction. These quasiparticles possess large dipole
moment due to the resonant coupling between direct and indirect excitons via electronic tunnelling. Using the
pulsed pumping of the cavity mode one can induce oscillations of the indirect exciton density. This corresponds
to a harmonic change of the dipole moment in time and results in the classical electromagnetic wave emission
with frequency being in the terahertz (THz) range. In the current paper we present a simple theory which
describes this phenomenon and estimate possible output power of radiation.
With the ability to grow multilayered structures down to atomic precision, the age of nanotechnology has begun. In particular, it has now become possible to realize structures with effective confinement of the electromagnetic field interacting efficiently with material excitations, and to achieve a strong coupling regime where the eigenmodes of the system, known as polaritons, have a hybrid half-light, half-matter character.
We revisit the intersubband polaritonics-the branch of mesoscopic physics, which has a huge potential for optoelectronic applications in the infrared and terahertz domains-and find that, contrary to the general opinion, the Coulomb interactions play a crucial role in the processes of light-matter coupling in the considered systems. Electron-electron and electron-hole interactions radically change the nature of the elementary excitations in these systems. We find that intersubband polaritons represent the result of the coupling of a photonic mode with collective excitations-and not noninteracting electron-hole pairs as it was supposed in the previous works on the subject.
A system where a Bose-Einstein condensate of exciton-polaritons coexists with a Fermi gas of electrons has been recently proposed as promising for realization of room-temperature superconductivity. In order to find the optimum conditions for exciton and exciton-polariton mediated superconductivity, we studied the attractive mechanism between electrons of a Cooper pair mediated by the exciton and exciton-polariton condensate. We also analyzed the gap equation that follows. We specifically examined microcavities with embedded n-doped quantum wells as well as coupled quantum wells hosting a condensate of spatially indirect excitons, put in contact with a two-dimensional electron gas. An effective potential of interaction between electrons was derived as a function of their exchanged energy ℏω, taking into account the retardation effect that allows two negatively charged carriers to feel an attraction. In the polariton case, the interaction is weakly attractive at long times, followed by a succession of strongly attractive and strongly repulsive windows. Strikingly, this allows high critical temperature solutions of the gap equation. An approximate three-steps potential is used to explain this result that is also obtained numerically. The case of polaritons can be compared with that of excitons, which realize the conventional scenario of high-Tc superconductivity where a large coupling strength accounts straightforwardly for the high critical temperatures. Excitons are less advantageous than polaritons but may be simpler systems to realize experimentally. It is concluded that engineering of the interaction in these peculiar Bose-Fermi mixtures is complex and sometimes counter-intuitive, but leaves much freedom for optimization, thereby promising the realization of high-temperature superconductivity in multilayered semiconductor structures.
We present the first findings of the transmission phase shift π/2 in the 0.7(2e2/h) structure of the quantum staircase and in the Kondo-correlated states revealed by an open system which represents a short quantum wire that is inserted within one of the arms of the Aharonov-Bohm (AB) ring inside the p-type self-assembled silicon quantum well prepared on the n-type Si (100) wafer. The quantum well of the p-type is naturally formed between δ-barriers by short-time diffusion of boron. The phase shift in the 0.7(2e2/h) structure caused by heavy holes is found to be changed from π to π by electrically-detected NMR of the 29Si nuclei thereby verifying the spin polarization in a quantum wire. The optical nuclear polarization of the 29Si nuclei induced by circularly polarized light in the n-type Si(100) wafer is shown to effect also on the coherent transport of holes through the quantum wire inserted within one of the AB ring's arms. The quantum conductance revealed by the quantum wire that is embedded in the AB ring inside self-assembled silicon quantum well in the weak localization regime is studied to demonstrate the coherence of the single-hole transport and negative magnetic resistance effect. The positive/negative transformation of the magnetoresistance in the weakest magnetic fields is found to be caused by the electrically-detected NMR of the 29Si nuclei thereby verifiying the effect of the nuclear spin polarization on a weak antilocalization.
The results of theoretical analysis of quasi one-dimensional electron gas within the Hartree-Fock approximation are presented. Ground state energies of completely polarized and non-polarized states are calculated at T equals 0. A formation of spontaneously spin-polarized state at low linear concentration of electrons and its transformation into non- polarized state as concentration grows are discussed.
In this work we present the results of the theoretical calculations of a ballistic conductivity of smooth and modulated quantum wires under nonideal conditions, i.e. at nonzero temperature and finite longitudinal bias. Deviations from the Landauer-Buttiker theory are described.
We present the findings of the quantized conductance in a modulated quantum wire. The energy dependence of the transmission coefficient through a smooth and modulated quantum wire is analyzed to define the role of elastic back scattering process in the formation of the conductance oscillations and the current staircase. We demonstrate the oscillations of 1D conductance plateaus as a function of drain-source voltage that are evidence of the interference effects caused by varying the energy of ballistic holes in the modulated quantum wire electrostatically created inside the silicon self-assembled quantum well. The Aharonov-Bohm (AB) rings prepared inside the silicon self-assembled quantum wells are used to study the interference of ballistic carriers tunneling through parallel quantum wires as a function of their length and modulation which are revealed by varying the external magnetic field and the drain-source voltage. The AB double-path interferometer defined by the quantum point contacts from the leads is found to exhibit the periodic oscillations in the quantized conductance that are evidence of the magnitude and phase of the transmission coefficient through the quantum wire embedded within the AB ring's arm.
We present the findings of quantized conductance (QC), Coulomb staircase (CS) and local tunneling spectroscopy (LTS) techniques which reveal the single-hole confinement and charging phenomena in the smooth and modulated quantum wires created electrostatically inside self-assembly longitudinal (SLQW) and lateral (SLaQW) silicon quantum wells. The current- voltage (CV) characteristics obtained are in a good agreement with the data of the theoretical calculations taking account of quantum interference effects in the field-dependent value of the transmission coefficient through the quantum wires that exhibit the different degree of a modulation.
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