Theory of ferromagnetic polariton linewidths

The interaction between magnons and photons which is responsible for magnetic polariton formation is expressed in terms of second quantized operators, and it is confirmed that the polariton dispersion curve obtained by diagonalizing the Hamiltonian is the same as that found classically. A term describing relaxation of the polariton by the two magnon mechanism which is often dominant in ferromagnetic resonance is then introduced. The lineshape function for inelastic light scattering is calculated by a Greens function technique. On the assumption that the lineshape can be approximated as a Lorentzian an expression for the linewidth is derived. The linewidth is zero when the polariton frequency Ω lies outside the magnon manifold, and increases discontinuously from zero at w = ¦γ¦H₀, where H₀ is the (internal) static field.     

Anomalously slow group velocity of upper branch polariton in CuCl

Group velocity of the Z₃ excitonic polariton was determined by measuring the propagation time of a picosecond light pulse in CuCl. Anomalously slow group velocity of the upper branch polariton was observed and the characteristic feature of the group velocity was qualitatively explained by taking account of the dispersion effect of the Z₁₂ exciton. This technique is available for the precise determination of the dispersion curve of the polariton.     

Raman scattering by the upper branch polariton in ZnO

The first observation of Raman scattering from the upper branch polariton in a semiconductor is reported. The significant reduction in collecting solid angle is the main cause that allows for this observation. The experimental polariton dispersion relation ω(K) can only be accounted for when dispersion is taken into consideration.     

Excitonic polariton dispersion in CuBr determined by resonant Raman scattering under two-photon excitation of excitonic molecules

The excitonic polariton dispersion in wide k-space for k∥[111] is measured through the two-photon-resonant Raman scattering with the use of the double beam excitation technique. The k-linear effect, the heavy and light masses and the polariton effect of the Z_1,2 exciton are clarified.     

Bound and many-particle states in polariton Raman spectra of NH4Cl crystals

The properties of polariton Raman spectra for the internal vibration region of NH₄Cl crystal are discussed. These spectra have been recorded by means of a copper laser ( $\text{λ = 5105 and 5782}\text{A}\text{?}$) for sample temperature T=80 and 10°K.According to the theory a polariton singularities in the region of a polar bound state has been obtained. The two-particle bands have been studied and a very complicate structure inside of these bands has been revealed. Moreover, multiphonon singularities at polariton curves have been observed. The experimental polariton law has been compared to the theory and a conclusion has been made as to the necessity of a further development of the theory.     

Influence of exciton decay on the polariton luminescence spectra of CdTe crystal

The polariton luminescence spectra of CdTe crystals have been numerically calculated with allowance for the decay of mechanical excitons and compared with the known experimental low-temperature photoluminescence spectra of these crystals. The mechanism of formation of polariton luminescence in dependence of the optical parameters of crystal for the exciton resonance A _n=1 is discussed.     

Polariton effect in degenerate valence band semiconductors

We present a model which describes excitonic polariton effect for direct gap semiconductors where the valence band is degenerate, so that two (“light” and “heavy”) exciton dispersion curves exist and give rise to three polariton branches. It is shown that the quantity $\text{δ = Δ ?}\text{1}\text{3}\text{E}{}_{\mathrm{LT}}$ is an important parameter in this case, Δ and E_LT being respectively the exchange energy and the longitudinal transverse splitting. A comparison with the available data, extracted from Resonant Brillouin Scattering in GaAs, is carried out. It is shown that when only the uppermost and lowest polariton branches can be detected, the measured separation Δ_exp between these two branches is equal to the longitudinal transverse splitting with a good approximation. In the general case the exact relation between Δ, E_LT and Δ_exp is derived.     

Coherent excitation of the soft polariton mode in BaTiO3

Coherent excitation of the soft polariton mode in BaTiO₃ is obtained by a two-beam method. The relative power variation on one beam is measured as a function of the polariton frequency (0 < ω_p < 30 cm^?1) for a scattering angle of 0.14° (|k_p| ? 4500 cm^?1) and shows a maximum at ω_p ? 13 cm^?1. By fitting experimental results to the theoretical power variations, the atomic displacive coefficient is determined.     

“Thermal barrier” effect in energy relaxation of polaritons in HgI2

The paper presents the results of measurements of polariton radiation spectra, polariton band excitation spectra and spectra of resonance Raman scattering HgI₂. These are registered at different temperatures and units of energetic derangement between the exciting radiation quantum energy and that of transverse exciton. The threshold value of the temperature (T=12 K) starting from which there is attained the equilibrium between the polariton and phonon subsystems is found. The scattering mechanism that guides the formation of “thermal barrier” favouring the polaritons thermalization, is revealed.     

Light scattering by polariton modes of KNbO3 in orthorhombic phase

The polariton modes of A₁, B₁ and B₂ species in biaxial KNbO₃ are observed by near forward Raman scattering. The oscillator strengths and dielectric constants along the principal axes are determined from the polariton dispersion. The mode assignments of each species are also discussed.     

Band-edge photoluminescence of PbI2

Photoluminescence spectra of the hexagonal layered semiconductor PbI₂ have been measured at 4.2°K on various single crystalline specimens. They are interpreted in relation with the anisotropic polariton model. The emitted radiation is assumed to originate from free and bound exciton recombination, with and without phonon emission. A peak polarized E ∥ c about 4 meV above the excitonic line is related to the extraordinary polariton mode.     

The mechanism of light emission from statistically rough tunnel junctions

Its is found that the spectrum of the light emitted by statistically rough tunnel junctions in the range 400–700 nm correlates with the calculated damping of the fast surface plasmon polariton mode of the tunnel junction structure. It is deduced that the radiative decay of this mode is responsible for the bulk of the light emission. It is shown that the view of existing theory that emission from statistically rough junctions is mediated by the slow surface plasmon polariton mode is untenable. Our deductions firmly consolidate a suggestion due to Kroo, Szentirmay and Felszerfalvi.     

Exciton polariton in an organic–inorganic multiple-quantum-well crystal (C4H9NH3)2PbBr4

Exciton polariton in an organic–inorganic multiple-quantum-well (MQW) single crystal (C₄H₉NH₃)₂PbBr₄ at low temperature has been investigated by photoluminescence excitation (PLE), reflection, and time-resolved photoluminescence measurements. Since (C₄H₉NH₃)₂PbBr₄ has ideal two-dimensional excitons with an extremely large oscillator strength and forms self-organized MQW with a very short well-period (d～10 Å), polaritonic coupling among excitons is strong and extends over a large number of wells. Therefore, observed MQW polariton features were the same as those of bulk polaritons. We have also investigated relaxation dynamics of the MQW polariton in the same framework as discussions on bulk polaritons.     

Microcavity polariton scattering probed by coherent control experiments

We present coherent control experiments which simultaneously probe both the coherence and the population dynamics of the exciton–photon polariton states in a semiconductor microcavity. The coherent manipulation of either the spin orientation or the density of polaritons is demonstrated leading to the measurement of the optical dephasing time. The polariton scattering by acoustical phonons or by mutual collision processes are investigated by a simultaneous measurement of both the optical dephasing time T₂and the decay time T₁of the radiant states. These results clearly evidence a quenching of the different scattering processes at resonance.     

Optical polariton properties in ZnSe-based planar and pillar structured microcavities

Strong coupling is demonstrated in monolithic ZnSe-based microcavities. Under nonresonant excitation the polariton dispersion has been investigated in dependence on the photon-exciton detuning for different excitation densities at low temperatures. For zero detuning indications of a polariton lasing threshold are observed like a k-space and energy dispersion narrowing of the lower polariton branch with increasing excitation density. Furthermore, it is observed that this effect is hampered for measurements at negative detunings as a result of the less effective polariton relaxation to the ground state. Latter results in the formation of a discrete polariton distribution at finite k values as known for the polariton bottleneck. In order to investigate the influence of a three-dimensional optical confinement on the polariton relaxation, pillar structured microcavities were fabricated. The formation of discrete polariton states in the k-space distribution is observed. Furthermore, indications for a softening of the k-conservation arising from the structural confinement are found leading to a more effective polariton relaxation. This process would be beneficial for the realization of efficient polariton lasing processes.     

Bulk and surface excitations in magnetoactive periodic semiconductor heterostructures

We have theoretically investigated the dispersion characteristics of bulk and surface excitations in a magnetoactive periodic semiconductor heterostructure (PSH) using a local theory in the nonretardation limit (c → ∞). The computation has been performed treating the unit cell of the heterostructure as made up of an array of alternate n-type GaAs (in A-type region) and n-type InSb (in B-type region) slabs of equal widths. The presence of the high magnetostatic field (B₀) gives a rich spectrum of the bulk excitations. A new type of surface polariton mode is found in a complete analogy with the one occurring at the surface of a semiconductor superlattice as predicted by Giuliani and Quinn. The frequency-dependent inverse penetration depth for this new magnetoplasma surface polariton has also been computed as a function of wave vector component parallel to the layers. We discuss our analytical and numerical results in the light of the recent work on heterostructures/superlattices.     

Phase sensitive spectroscopy of the polariton modes in a ZnSe-ZnSxSe1−x heterostructure

Applying the method of spectral interferometry we investigate the phase of reflected light at a ZnSe-ZnS_xSe_1−x heterostructure. We find a series of polariton modes propagating through the ZnSe layer. They can be related to the different polariton branches split of at the heavy- and light-hole excitons. The phase shows pronounced changes around these modes. The strongest changes by 2π appear at the modes of lowest order located weakly above the exciton resonances, while they are smaller for higher modes. Our experimental findings can be explained considering spatial dispersion, Pekar's additional boundary conditions and a weak extension of the excitonic polarization into the ZnS_xSe_1−x cladding layers.     

Surface phonon–polaritons in rectangular quantum wires of polar ternary mixed crystals

In this paper, the dispersion relations of surface phonon–polaritons in freestanding rectangular quantum wire systems of polar ternary mixed crystals are derived. The numerical calculations for Al_xGa_1−xAs and Zn_xCd_1−xSe quantum wire systems are performed. The results reveal that the frequencies of surface phonon–polariton modes are sensitive to the geometric structures of the quantum wires, the wave-vectors in z-direction, and the compositions of the ternary mixed crystal materials. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface phonon–polariton modes are also discussed.     

Scattering of an exciton polariton by impurity centers in GaAs

Scattering of an exciton polariton by impurity centers at low temperatures has not been investigated comprehensively in spite of its significant role in processes accompanying Bose–Einstein condensation of an exciton polariton. For studying the peculiarities of the interaction of an exciton polariton with impurity centers, we have studied the integrated absorption of the ground state (n ₀ = 1) of the exciton in GaAs in thin (micrometer-thick) wafers with an appreciable optical transmission. Comparative analysis of the transmission in the vicinity of the exciton resonance performed on 15 samples of crystalline GaAs wafers with different concentrations N of impurity has revealed an unexpected regularity. The value of N increases by almost five decimal orders of magnitude, while the normalized spectrally integrated absorption of light exhibits a slight increase, following the power dependence N ^m on the concentration, where m = 1/6. It has been shown that this dependence indicates the diffusion mechanism of propagation of the exciton polaritons through the bulk of the semiconductor, which is present along with the ballistic propagation of light through the sample.     

Anisotropic polariton dispersion in red HgI2

We have measured resonant Brillouin Scattering near the A-exciton region of a layer-semiconductor, red-HgI₂. The Brillouin shift is interpreted in terms of a scattering process between the two polariton states by an acoustic phonon. The estimated exciton masses for the translational motion are (0.68 ± 0.1)m₀ and (1.2 ± 0.1)m₀ for the (100 and (001) directions, respectively.