Gap kinematic Frenkel biexciton

A general dispersion equation is derived determining the wave-vector dependence of the energy of a bound kinematic Frenkel biexciton, previously discovered by the author, in crystals of arbitrary symmetry. A solution of this equation shows that, in crystals of a certain symmetry, bound gap Frenkel biexcitons can exist, the isolated terms of which lie in the gap between the components of the Davydov multiplet of unbound two-exciton states. In crystals with two monomers in the unit cell, these terms lie in the gap between two low-frequency components of the Davydov multiplet and are not in resonance with the central component, in contrast to what was observed in previously investigated crystals of higher symmetry. Besides, the biexcitons discovered in this work have a finite, rather than zero, dispersion, although their bandwidth is extremely small. The bound biexcitons also have some other specific features followed from the dispersion relation.     

The laser-Raman spectrum of a Davydov soliton

It is suggested that the laser-Raman spectra between 30 and 300 cm^?1, which have recently been observed on metabolically active cells, may reflect the internal vibrations of Davydov solitons.     

Direct two-photon creation of a biexciton

The nonlinear absorption coefficient for the two-photon creation of biexciton in CuCl is calculated in the approximation of one intermediate, optically active excitonic state. The two-band model with realistic band structure at the band extrema is considered. The exciton-biexciton dipole transition momentum matrix element is expressed by the functional of the exciton and biexciton envelopes. In the numerical calculations the envelope of the Hylleraas-Ore type, modified by Brinkman et al., is used. Our calculated value of the absorption coefficient is about two orders of magnitude smaller than that estimated previously by Hanamura, and agrees better with the experimental value reported by Gale and Mysyrowicz.     

Vibronic Frenkel exciton in a soft-mode crystal

The pair electron-hole Jahn-Teller effect, which is realized on degenerate states of a vibronic Frenkel exciton (VFE) in soft-mode crystals, is considered. It is shown that the vibronic effect in a VFE can be significantly enhanced in crystals having soft lattice modes. The occurrence of strong local order-disorder fluctuations in this situation is predicted. The manifestations of VFEs localized at impurities in soft matrices (Cr³⁺ in SrTiO₃, Fe⁵⁺ in KTaO₃, and Mn⁵⁺ in TbVO₄ and TbPO₄) are considered. The possibility of fluctuation effects related to VFEs in nominally pure soft-mode crystals (SrTiO₃ and BaTiO₃) is discussed.     

Optical absorptions of a biexciton quantum dot

A investigation of the linear and nonlinear optical properties for intersubband electronic transitions associated with a biexciton in a quantum dot has been performed by using the method of few-body physics. The optical absorption coefficients and the refractive index changes have been examined based on the computed energies and wave functions. It is over two orders of magnitude higher than that obtained in an exciton quantum dot. The results show that the optical absorption saturation intensity can be controlled by the confinement potential frequency and the relaxation time.     

The density multiplet in superspace

We calculate the components of the density multipletE inN=1 superspace and the last component of the chiral density multiplet ? inSU(2) extended superspace with a minimal set of auxiliary fields.     

Effect of interchain coupling on a biexciton in organic polymers

The effect of interchain coupling on the formation and the stability of a biexciton is studied in poly (p-phenylene vinylene) chains in the framework of the tight-binding approach. We obtain an intrachain exciton and biexciton as well as an interchain exciton and biexciton through a double-photon excitation. It is found that a biexciton is energetically favourable to two single excitons even when there exists an interchain coupling. There is a turnover value t_⊥C of the interchain coupling for the formation of a biexciton, beyond which two excitons are combined into one biexciton. The binding energy of a biexciton is calculated to decrease with the increase of interchain coupling, which indicates that a biexciton is relatively stable in polymers with a weak interchain coupling. The conclusion is consistent with the experimental observations. In addition, a suggestion about how to improve the yielding efficiency or the formation of biexcitons in actual applications is given.     

Protein as a system of interacting Frenkel excitons

We propose an alternative mechanism for the self-localization of the energy of amide-I vibrations in α-helical proteins. We generalize the Davydov Hamiltonian for the amide-I excitons to include the exciton-exciton interactions and show analytically and numerically that there exist modulational instability and nonlinear localized modes in this system. We also show that the dynamics of the initial pulses is sensitive to the symmetries of their shapes.     

Eigenstate symmetry probed by biexciton transitions in a single quantum dot

The eigenstate symmetry in CdSe/ZnSe single quantum dots (SQDs) has been studied by low-temperature magnetoluminescence spectroscopy. Regarding both, the fine structure splitting and the polarization properties of the biexciton transition, the influence of exchange and Zeeman interaction on the eigenstate symmetry of the final state of recombination, the ground state of the single exciton, is investigated.     

Efficient two-photon light amplification by a coherent biexciton wave

A reversible coupling between photon pair states and a long-lived, highly coherent biexciton wave in CuCl allows efficient phase-sensitive two-photon amplification or attenuation of ultrashort light pulses. We demonstrate a gain of 350 cm(-1) for a pump intensity of 1 MW/cm(2), nearly 2 orders of magnitude higher than that achievable with conventional parametric crystal amplifiers. We develop a theoretical model that describes this new type of parametric converter where the light pump is replaced by a coherent biexciton wave and show that it is well suited for the generation of entangled photons and the squeezing of an optical beam with ultrafast time gating.     

Many-exciton effects in the biexciton bound-state potential

Starting from a previously derived many-particle equation describing biexciton states, the influence of dynamical exciton-exciton scattering effects on the biexciton binding energy has been calculated. As a result, we obtain density effects in bound states. In qualitative agreement with experimental data only a small density-induced shift of the biexcitonic luminescence should be observed.     

Davydov splitting and rigid-layer modes in InS crystal

Polarized infrared reflection spectra of InS layer crystal have been measured. Both components of the Davydov doublets caused by the splitting of intralayer vibrations due to the interlayer interactions are active in i.r. spectra. Doublet frequencies have been used to calculate the rigid-layer mode frequencies which are correlated with the experimental ones. It has been established that in InS crystal the frequencies of rigid-layer modes are much higher than those of ordinary layer crystals. Atomic displacements have been found at i.r.-active normal modes.     

The Frenkel effect in semiconductor diodes

A possible explanation is postulated of the experimentally observed (under certain conditions) dependence of the reverse current of geranium and silicon diodes on the applied voltage. The explanation is based on a supposition that the probability of the generation of electrons and holes by recombination centers in the zone of the volume charge of a p-n junction (to which an inverse voltage is applied) is increased due to the thermal ionization being facilitated by the electric field.     

Quantum-chemical simulation of Frenkel pairs separation in a LiF crystal

Semiempirical quantum-chemical (INDO) simulation of the creation of the primary Frenkel pairs of defects in a LiF crystal based on the Pooley-Smoluchowski mechanism of the self-trapped exciton annihilation has been undertaken. The conclusion has been drawn that this mechanism can be operative from the viewpoints of both the time and the energy needed to create the F, H pair in terms of this mechanism. Unlike the Toyozawa's model an initial vibrational excitation is not bottleneck of the decay process (cf. [8]).     

Correspondence between the three-form and a non-minimal multiplet in supersymmetry

In analogy to the chiral–linear multiplet correspondence we establish a relationship between the 3-form(or gaugino condensate) multiplet and a coupled non-minimal (0,1/2) multiplet, illustrated by a simple explicit example. PACS 11.30.Pb     

Fine-structure quenching and multiplet distortion in a screened Coulomb atom

Theoretical results presented in this paper reflect that the relativistic fine-structure due to the mass-velocity, spin-orbit and Darwin terms is sensitive to the screening strength parameter in an exponential screened Coulomb hydrogen atom, that is sometimes used to model a plasma-embedded atom. With stronger screening the fine-structure correction undergoes a gradual suppression in magnitude, but contributes to the total binding energy in an increasing proportion, indicating that the relativistic contribution to binding may become quite significant in the ultra-low binding regime under large screening strength. In the presence of screening the l-independence of the fine-structure correction as predicted by the Dirac theory progressively disappears, and a departure from the Z⁴-scaling law of the correction occurs along the H-isoelectronic sequence of ions - both the effects become accentuated with growing screening strength. In conjunction with screening-induced removal of the Coulomb degeneracy of non-relativistic levels, these result in a deformed multiplet structure for the screened Coulomb atom. Received 31 May 1999 and Received in final form 20 September 1999     

Electromagnetically induced transparency in semiconductors via biexciton coherence

We report an experimental demonstration and theoretical analysis of electromagnetically induced transparency in a GaAs quantum well, in which the absorption of an exciton resonance is reduced by more than twentyfold. The destructive quantum interference in this scheme is set up by a control pulse that couples to a resonance of biexcitons. These studies illustrate that many-particle interactions, which are inherent in semiconductors and are often detrimental to quantum coherences, can also be harnessed to manipulate these coherences.     

Particle octupole multiplet in147Gd

The rotational properties of the odd-odd¹⁶⁸Tm have been studies by means of the¹⁶⁵Ho(α, 3n)¹⁶⁶Tm reaction. The existence of five rotational bands has been established.     

Stimulated emission from the biexciton in a single self-assembled II-VI quantum dot

Using two-photon excitation, stimulated emission from the biexciton state in a single CdSe/ZnSe quantum dot is observed in a two-pulse configuration. We directly time resolve the emission-absorption characteristics and verify the potential for laser action. By setting the polarization of the stimulation pulse, the recombination path of the biexciton and, by this, the state of the photons emitted in the decay cascade is controlled. We elaborate also the coherent response and address entanglement and disentanglement of the exciton-biexciton system.