Longitudinal-transverse Splitting Research Articles

Chiral solitons in spinor polariton rings

We consider theoretically one-dimensional polariton ring accounting for both longitudinal-transverse (TE-TM) and Zeeman splitting of spinor polariton states and spin dependent polariton-polariton interactions. We present the novel class of solutions in the form of the localized defects rotating with constant angular velocity and analyze their properties for realistic values of the parameters of the system. We show that the effects of the geometric phase arising from the interplay between external magnetic field and TE-TM splitting introduce chirality in the system and make solitons propagating in clockwise and anticlockwise directions non equivalent. This can be interpreted as solitonic analog of Aharonov-Bohm effect.

Phonon states of B12P2 crystals: Ab initio calculation and experiment

Using methods of density functional theory (DFT) and Raman spectroscopy (RS) we investigate the phonon structure of the B12P2 crystal. The theory is consistent with the experiment for all twelve Raman-active modes. We have calculated Born charges, oscillator strengths, longitudinal-transverse splitting, and dielectric functions of dipole modes. The results are used to interpret the known IR spectra of B12P2. Analysis of phonon dispersion shows that the crystal is dynamically stable. The energy gap separating acoustic and optical phonons is absent due to the overlap of the phonon states at the Brillouin zone boundary. Vibrations of phosphorus and boron atoms contribute to the low- and high-frequency regions of the phonon density of states, respectively.

On the theory of three types of polaritons (phonon, exciton and plasmon polaritons)

We have investigated the similarities and difference between three well-known types of polaritons: phonon polariton, exciton polariton and surface plasmon polariton. For first two types (phonon polariton and exciton polariton) the interaction between photon and media can be expressed via a longitudinal-transversal splitting (LT-splitting), while for third type of polariton (surface plasmon polariton) via the boundary condition. Considering an analogy of these three types of polaritons, an effective LT-splitting was introduced for surface plasmon polariton. We discuss a possible existence of an evanescent state in the band gap of polaritons. Finally, the Nambu broken symmetry theory and Anderson-Higgs mechanism are discussed for lower branch of these polaritons.

Phonon and electronic properties of the LiCaAlF6 crystal: Experiment and ab initio calculations

We have studied the IR polarized reflection spectra of LiCaAlF6 crystal in the range of 50–2000 cm–1 and have obtained parameters of dipole phonons. In order to calculate the electronic and vibrational properties of the crystal, we have applied the density functional method with the basis sets of Gaussian functions and plane waves. We have shown that the structure of electronic bands has a direct energy gap. The projected densities of electronic states of atoms, the Born effective charges, and the Mulliken populations have been found to be consistent with the ionic–covalent character of cation–fluorine interatomic bonds. The dielectric properties in high and low-frequency limits have been calculated. We have examined the longitudinal–transverse splitting of dipole modes and have revealed a phonon with an inverted splitting. The theoretical IR reflection and Raman spectra have been found to agree well with experiment. Based on the analysis of the dispersion of phonons in the Brillouin zone, we have revealed an effect of the “quasi-doubling” of the crystal cell along the z axis due to the competing interactions of atoms with nearest and next neighbors. We have found that phonons with frequencies higher than 500 cm–1 are separated by an energy gap and have predominantly stretching character of vibrations.

The hydrogen-bond network of water supports propagating optical phonon-like modes.

The local structure of liquid water as a function of temperature is a source of intense research. This structure is intimately linked to the dynamics of water molecules, which can be measured using Raman and infrared spectroscopies. The assignment of spectral peaks depends on whether they are collective modes or single-molecule motions. Vibrational modes in liquids are usually considered to be associated to the motions of single molecules or small clusters. Using molecular dynamics simulations, here we find dispersive optical phonon-like modes in the librational and OH-stretching bands. We argue that on subpicosecond time scales these modes propagate through water's hydrogen-bond network over distances of up to 2 nm. In the long wavelength limit these optical modes exhibit longitudinal–transverse splitting, indicating the presence of coherent long-range dipole–dipole interactions, as in ice. Our results indicate the dynamics of liquid water have more similarities to ice than previously thought.

Spin currents of exciton polaritons in microcavities with (110)-oriented quantum wells

We study the polarization optical properties of microcavities with embedded (110)-oriented quantum wells. The spin dynamics of exciton polaritons in such structures is governed by the interplay of the spin-orbit splitting of exciton states, which is odd in the in-plane momentum, and the longitudinal-transverse splitting of cavity modes, which is even in the momentum. We demonstrate the generation of polariton spin currents by linearly polarized optical pump and analyze the arising polariton spin textures in the cavity plane. Tuning the excitation spot size, which controls the polariton distribution in the momentum space, one obtains symmetric or asymmetric spin textures.

Giant Rabi Splitting of Whispering Gallery Polaritons in GaN/InGaN Core-Shell Wire.

The hybrid nature of exciton polaritons opens up possibilities for developing a new concept nonlinear photonic device (e.g., polariton condensation, switching, and transistor) with great potential for controllability. Here, we proposed a novel type of polariton system resulting from strong coupling between a two-dimensional exciton and whispering gallery mode photon using a core-shell GaN/InGaN hexagonal wire. High quality, nonpolar InGaN multiple-quantum wells (MQWs) were conformally formed on a GaN core nanowire, which was spatially well matched with whispering gallery modes inside the wire. Both high longitudinal-transverse splitting of nonpolar MQWs and high spatial overlap with whispering gallery modes lead to unprecedented large Rabi splitting energy of ∼180 meV. This structure provides a robust polariton effect with a small footprint; thus, it could be utilized for a wide range of interesting applications.

All optical controlled-NOT gate based on an exciton–polariton circuit

We propose an implementation of a CNOT gate for quantum computing based on a patterned microcavity polariton system, which can be manufactured using the modern technological facilities. The qubits are encoded in the spin-coherent polariton states. The structure consists of two wire cavities oriented at 45° with a micropillar between them. The polariton spin rotates due to the Longitudinal–Transverse splitting between polarization eigenstates in the wires. In the pillar, the optically generated circularly polarized polariton macrooccupied state plays the role of the control qubit. Because of the spin-anisotropic polariton interaction, it induces an effective magnetic field along the Z-direction with a sign depending on the qubit value.

Spontaneous electric fields in solid carbon monoxide.

Reflection-absorption infrared spectroscopy (RAIRS) is shown to provide a means of observing the spontelectric phase of matter, the defining characteristic of which is the occurrence of a spontaneous and powerful static electric field within a film of material. The presence of such a field is demonstrated here through the study of longitudinal-transverse optical splitting in RAIR spectra in films of carbon monoxide, based upon the deposition temperature dependence of this splitting. Analysis of spectral data, in terms of the vibrational Stark effect, allows the measurement of the polarization of spontelectric films, showing for example that solid carbon monoxide at 20 K may maintain a spontelectric field of 3.78 × 10(7) V m(-1), representing a polarization of 3.34 × 10(-4) cm(-2). We comment on the astrophysical implications of polarized carbon monoxide ices, on the surface of cosmic grains in star-forming regions.

Dependence of the Structure, Optical Phonon Modes and Dielectric Properties on Pressure in Wurtzite GaN and AlN

The density functional perturbation theory (DFPT) is employed to study the structure, optical phonon modes and dielectric properties for wurtzite GaN and AlN under hydrostatic pressure. In order to calculate accurately the Born effective charges and high frequency dielectric tensors, we utilize two sum rules to monitor this calculation. The calculated optical phonon frequencies and longitudinal-transverse splitting show an increasing with pressure, whereas the Born effective charges and high frequency dielectric tensors are found to decrease with pressure. In particular, we analysed the reason for discrepancy between this calculation and previous experimental determination of pressure dependence of the LO-TO splitting in AlN. The different pressure behavior of the structural and lattice-dynamical properties of GaN and AlN is discussed in terms of the strengths of the covalent bonds and crystal anisotropy. Our results regarding dielectric Gruneisen parameter are predictions and may serve as a reference.

Longitudinal–transversal polariton splitting on a GaAs single quantum well microcavity

Exciton polariton is a quasi-particle formed in a microcavity, which keeps the exciton and the photon property, e.g. the exciton longitudinal–transversal energy splitting. In this work we observed a splitting as large as 0.19meV in the polariton emission mode in a GaAs single quantum well microcavity for the heavy hole as well as a 0.137meV for the light hole excitons. The splitting behavior was analyzed as a function of excitation power and the polarization degree. The results indicate one longitudinal–transversal splitting emission light with mixed spin states and crossed linear polarizations for the longitudinal–transversal modes, and a condensation behavior only for the heavy hole transversal mode.

Motion of patterns in polariton quantum fluids with spin-orbit interaction

We report on a remarkable effect of pseudospin precession on the collective motion of exciton-polaritons in a microresonator coherently driven by a linearly polarized pump. In particular, we show that hexagonal patterns can undergo a spontaneous symmetry breaking of their polarization and start a uniform motion in the plane of the resonator. Similar to the optical spin Hall effect, this becomes possible due to a spin-orbit interaction induced by a longitudinal-transverse splitting (TE-TM splitting) of the photonic resonator mode. We derive a simple analytical expression for the drift velocity of the patterns.

Effects of strain on the valence band structure and exciton-polariton energies in ZnO

The uniaxial stress dependence of the band structure and the exciton-polariton transitions in wurtzite ZnO is thoroughly studied using modern first-principles calculations based on the HSE+G0W0 approach, k p modeling using the deformation potential framework, and polarized photoluminescence measurements. The ordering of the valence bands [A(G7), B(G9), C(G7)] is found to be robust even for high uniaxial and biaxial strains. Theoretical results for the uniaxial pressure coefficients and splitting rates of the A, B, and C valence bands and their optical transitions are obtained including the effects of the spin-orbit interaction. The excitonic deformation potentials are derived and the stress rates for hydrostatic pressure are determined based on the results for uniaxial and biaxial stress. In addition, the theory for the stress dependence of the exchange interaction and longitudinal-transversal splitting of the exciton-polaritons is developed using the basic exciton functions of the quasi-cubic approximation and taking the interaction between all exciton states into account. It is shown that the consideration of these effects is crucial for an accurate description of the stress dependence of the optical spectra in ZnO. The theoretical results are compared to polarized photoluminescence measurements of different ZnO substrates as function of uniaxial pressure and experimental values reported in the literature demonstrating an excellent agreement with the computed pressure coefficients.

Strong Renormalization of the Electronic Band Gap due to Lattice Polarization in theGWFormalism

The self-consistent GW band gaps are known to be significantly overestimated. We show that this overestimation is, to a large extent, due to the neglect of the contribution of the lattice polarization to the screening of the electron-electron interaction. To solve this problem, we derive within the GW formalism a generalized plasmon-pole model that accounts for lattice polarization. The resulting GW self-energy is used to calculate the band structures of a set of binary semiconductors and insulators. The lattice contribution always decreases the band gap. The shrinkage increases with the size of the longitudinal-transverse optical splitting and it can represent more than 15% of the band gap in highly polar compounds, reducing the band-gap percentage error by a factor of 3.

Temperature-dependent integral exciton absorption in semiconducting GaAs crystals

The temperature dependence of the fundamental absorption edge in free-standing “epitaxial” InP layers has been experimentally studied. The integral exciton absorption coefficient K(T) exhibits an increase at low temperatures, which is explained in terms of the exciton-polariton mechanism of light transfer in semi-conductor crystals with spatial dispersion. A critical temperature (T c = 200 K), above which the integral absorption becomes constant, has been experimentally determined, and the corresponding critical decay parameter (Γc = 0.341 meV), longitudinal-transverse splitting (ħωLT = 0.175 meV), and oscillator strength of the exciton transition (β = 0.237 × 10−4) have been calculated. The temperature dependence of the true dissipative decay has been determined.

Spin multistability in dissipative polariton channels

We present a model for theoretical description of the dynamics of a system of spinor cavity polaritons in real space and time accounting for all relevant types of the interactions and effective magnetic fields. We apply our general formalism for the consideration of the polarization dynamics of the coherently driven one dimensional polariton channel. We investigate effect of the temperature and the longitudinal-transverse splitting on the spin (polarization) multistability and hysteresis arising from the polarization-dependent polariton-polariton interaction. We show that the effect of the phase of the driving laser pump is as important as its strength and demonstrate that the multistability behavior can survive up to high temperatures in presence of longitudinal-transverse splitting.

On the νSiO infrared absorption of polysiloxane films

The infrared absorption of polysiloxanes involves a strong band at around 1050cm−1, attributed to the antisymmetric vibration of siloxane bridges. The splitting of this band into two components is generally attributed to coupling between next-neighbor siloxane groups along the polysiloxane chain. From a quantitative analysis of the spectra of these materials, we find that this splitting is larger when the material is in thin-film form, and that the relative intensity of the two components is polarization dependent. We show that these effects are fully understandable in the theoretical framework of infrared absorption by thin films, and are related to long-range dipolar interactions responsible for the longitudinal–transverse splitting effect in crystalline materials. As a consequence, the polarization dependence of the infrared absorption observed for thin films does not appear to be associated with an orientational ordering in the film.

Lyddane-Sachs-Teller Relationship in Linear Magnetoelectrics

In a linear magnetoelectric the lattice is coupled to electric and magnetic fields; both affect the longitudinal-transverse splitting of zone-center optical phonons on equal footing. A response matrix relates the macroscopic fields (D, B) to (E, H) at infrared frequencies. It is shown that the response matrices at frequencies 0 and ∞ fulfill a generalized Lyddane-Sachs-Teller relationship. The right-hand side member of such relationship is expressed in terms of weighted averages over the longitudinal and transverse excitations of the medium, and assumes a simple form for a harmonic crystal.

Spin and transport effects in quantum microcavities with polarization splitting

Transport properties of exciton-polaritons in anisotropic quantum microcavities are considered theoretically. Microscopic symmetry of the structure is taken into account by allowing for both the longitudinal-transverse (TE-TM) and anisotropic splitting of polariton states. The splitting is equivalent to an effective magnetic field acting on polariton pseudospin, and polarization conversion in microcavities is shown to be caused by an interplay of exciton-polariton spin precession and elastic scattering. In addition, we considered the spin-dependent interference of polaritons leading to weak localization and calculated coherent backscattering intensities in different polarizations. Our findings are in a very good agreement with the recent experimental data.

Fraction of a Millimeter Propagation of Exciton Polaritons in Photoexcited Nanofibers of Organic Dye

We report propagation of exciton polaritons (EPs) in photoexcited nanofibers of thiacyanine dye over a few hundred micrometers at room temperature. We determine the complex refractive index along the nanofibers by fluorescence microscopy measurements on single nanofibers and observe its anomalous behavior due to the EP effect. The longitudinal-transverse splitting energy (ΔE(L-T)) is evaluated to be ∼1 eV. The large ΔE(L-T) and waveguide function of the nanofibers allow a millimeter propagation of EPs at room temperature, which is hardly realized in other systems.