Translation invariant theory of polaron (bipolaron) and the problem of quantizing near the classical solution

A physical interpretation of translation-invariant polarons and bipolarons is presented, some results of their existence are discussed. Consideration is given to the problem of quantization in the vicinity of the classical solution in the quantum field theory. The lowest variational estimate is obtained for the bipolaron energy E(η) with E(0) = -0.440636α², where α is a constant of electron-phonon coupling, η is a parameter of ion binding.     

Temperature dependence of quantal and thermal dampings of the hot giant dipole resonance

A systematic study of the damping of the giant dipole resonance (GDR) in ⁹⁰Zr, ¹²⁰Sn and ²⁰⁸Pb as a function of temperature T is performed. The double-time Green function technique is employed to determine the single-particle and GDR dampings. The single-particle energies, obtained in the Woods-Saxon potential for these nuclei, are used in the calculations. The results show that the coupling of collective vibration to the pp and hh excitations, which causes the thermal damping width, is responsible for the enlargement of the total width with increasing temperature up to T ≈ 3MeV and its saturation at higher temperatures. The quantal width, which arises from the coupling of the collective mode to the ph excitations decreases slowly with increasing temperature. The effect of single-particle damping on the GDR width is small. The results are found in an overall agreement with the experimental data for the GDR width, obtained in the inelastic α scattering and heavy-ion fusion reactions at excitation energies E^* ⩽ 450 MeV. At high excitation energies (E^* > 400 MeV) a behavior similar to the transition from zero to ordinary sounds is observed.     

On the structure of wave fields in the region of linear interaction between ordinary and extraordinary waves in two-dimensionally inhomogeneous magnetoactive plasmas

The spectra of the low-temperature photodissociation (photoionization) of Landau-Pekar polarons are calculated using the theory of quantum-coherent states and a new method of variation with respect to the parameters of phonon vacuum deformation. It is shown that the final polaron states upon photodissociation may have different numbers of phonons produced in a single dissociation event and different momenta of charge carriers. The spectrum of optical absorption related to the photodissociation of polarons exhibits a superposition of bands corresponding to various numbers of phonons formed as a result of dissociation of a single polaron. Due to a large width of the energy region corresponding to the final states of charge carriers, the halfwidth of each band is on the order of the energy of polaron coupling and is much greater than the phonon energy. For this reason, the individual phonon bands exhibit strong overlap. The very broad and, probably, structureless band formed as a result of the superposition of all these components begins at an energy equal to the sum of the polaron coupling energy (E _p) and the phonon energy. This band has a maximum at a frequency of about 5.6E _p/? and a halfwidth on the order of 5.6E _p/? at a unit effective mass (m* = m _e) of band electrons. For an effective charge carrier mass within m* = (1–3)m _e, the energy of the polaron band maximum can be estimated as 5E _p with an error of about 10%, and the halfwidth falls within 3.4E _p < ?Ω_1/2 < 5.6E _p. The multiphonon character of this band is related to a decay of the phonon condensate after the escape of charge carrier from a polaron. Such polarons are likely to be observed in the spectra of complex metal oxides, including high-temperature superconductors. Examples of such polaron bands in the reported absorption and photoconductivity spectra of nonstoichiometric cuprates, manganites, nickelates, and titanates are presented. A theory of the formation of Landau-Pekar polarons with the participation of branches of the polarization oscillations of the medium is developed. It is shown that, under certain conditions, such a multiphonon-dressed polaron can possess a coupling energy on the order of 0.2–0.3 eV, so that the maximum of the corresponding absorption band may occur at 1–1.5 eV.     

Disappearance of the hindrance ofE1-transition involving loosely bound nucleon

AlthoughE1-transition between levels below giant dipole resonance are almost always strongly hindered, there are several exceptions as observed in¹¹Be and¹³C. These fastE1-transitions are studied by adopting a simple “cutoff” model, in which the behavior of single particle wave functions only outside of the nucleus contribute. The results are compared with the particle-GDR coupling model. The reason why theE1-hindrance disappears is explained. We also investigate the direct capture of thermal neutron by⁴⁰Ca andN=82 nuclei, where similar situation is observed. Further, the implication of the direct capture in multiple neutron capture is discussed.     

Dynamical treatment of quenching-factors (Ham-factors) for the linear E-e Jahn-teller problem

The quenching factors for the linear E-e Jahn-Teller system are calculated by use of the exponential transformation method. In the extremal coupling cases the results are identical with those of Ham [1] and others [2]. For intermediate interactions, however, the factors p and q do not exhibit a monotonic overall decrease with increasing coupling strength, as suggested by Ham. Instead, both p and q have a minimum. In addition, p crosses the zero axis for λ ≌ 0.66.     

Projected Hartree-Fock calculation in intermediate coupling for11B

An intermediate coupling calculation has been carried out for¹¹B using the deformed functions obtained from a Projected Hartree-Fock calculation as a basis. The resulting wave functions give an important improvement for the energy spectrum of the low-lying nonnormal parity levels. TheE2 matrix elements are enhanced with respect to the conventional shell model. Nuclear structure¹¹B; calculated levelsJ, π, B(M1),B(E2). Projected Hartree-Fock method, intermediate coupling.     

Coupling of giant resonances via residual interactions

The coupling between E2 and M1 modes in deformed ¹⁵⁴Sm is investigated within the novel averaging RPA approach with the factorized residual interaction. The calculations show that the E2 giant resonance is not noticeably affected by the coupling. At the same time, the M1 response demonstrates a new structure (high-energy branch of the scissors mode) at 24–25 MeV.     

Search for a parity violation induced by neutral currents in the 6S–7S transition of atomic cesium

Parity violating, time-reversal invariant, weak neutral currents can induce an electric dipole transition moment, E₁^p.v., between atomic states of same parity. We report here on the preliminary results of an experiment designed to measure E₁^p.v. in the 6S–7S transition of atomic cesium, using a polarization effect characteristic of the interference of E₁^p.v. with the electric dipole transition moment E₁^ind. induced by a d.c. electric field. At a 90% confidence level we find the upper limit: |E₁^p.v.| < 2.0 × 10^?9|e|a₀. As a consequence the coupling constant of the electron-nucleon interaction involving the product of an axial electronic neutral current by a vector nucleonic one must be less than 44 G_F.     

Doppler-free spectroscopy of the 8s state of Cs

Doppler-free two-photon spectroscopy and ion detection in a thermionic diode were used to measure the hyperfine splitting and absolute term energy of the 8S state of Cs. The results, a=219.3(2) MHz for the magnetic dipole coupling constant, and E(8S)=24317.1499(4) cm^-1 for the term value of the c.g. of the 8S state relative to the c.g. of the ground state, agree well with earlier, less precise measurements. The hyperfine coupling also agrees well with a recent relativistic Hartree-Fock calculation.     

k-linear coupling and the E′1 transitions in GaAs

The k-linear intravalence and intraconduction band coupling terms along the 〈111〉 directions are shown to explain the anomalously large strength of the E′₁ structure relative to E′₁ + Δ′₁ and also the large energy separation between them. Quantitative agreement between theory and experiment is obtained using intraband coupling values calculated from k · p perturbation theory.     

Accurate energy levels for the anharmonic oscillator and a summable series for the double-well potential in perturbation theory

We introduce a generalization of Wick-ordering which maps the anharmonic oscillator (AO) Hamiltonian for mass m and coupling λ exactly into a “Wick-ordered” Hamiltonian with an effective mass M which is a simple analytic function of λ and m. The effective coupling $\text{Λ =}\text{λ}\text{M}{}^3$ is bounded. We transform the AO perturbation series in λ into one in Λ. This series may then be summed using Borel summation methods. We also introduce a new summation method for the AO series (which is a practical necessity to obtain accurate energy levels of the excited states). We obtain a numerical accuracy for $\text{(E}{}_{\mathrm{PT}}\text{? E}{}_{\mathrm{exact}}\text{)}\text{E}{}_{\mathrm{exact}}$ of at least 10^?7 (using 20 orders of perturbation theory) and 10^?3 (using only 2 orders of perturbation theory) for all couplings and all energy levels of the anharmonic oscillator. The methods are applicable also to the double-well potential (DWP, the AO with a negative mass-squared). The only change is that now the effective coupling is unbounded as λ → 0. The series in Λ is, however, still summable. The relative accuracy in the energy levels for 20 orders of perturbation theory varies from 10^?7 for large coupling to 1% at λ = 0.1 and to 10% at λ = .05. We also present results for the sextic oscillator.     

Interplay of valence-shell clusters and the vibrational field in205Pb and206Pb

The properties of²⁰⁵Pb and²⁰⁶pb are described in the cluster vibrational field coupling model. Excitation energies, strengths for one-particle transfers,E2 andM1 observables are compatible with the available experimental data. Other theoretical approaches for these nuclei are discussed and compared with the results of the present investigation.     

On the study of the vibrational energy levels of Arsine molecule

We compare two formalisms applied to the vibrational modes of the molecule of AsH₃ of C_3v molecular symmetry group. Indeed, the close stretching modes of this molecule may be considered as those of a three-dimensional oscillator whereas the bending modes may be considered either as a one-dimensional oscillator of symmetry A₁ and a two-dimensional oscillator of symmetry E or as an approximate three-dimensional oscillator. So, we have applied the U(p + 1) formalism to the both stretching and bending modes and introduced coupling terms acting on an appropriate coupled vibrational basis through a local mode formalism. We have then compared the result of our fitting with those obtained with the coupling of a local mode formalism adapted to the stretching vibrations with a normal mode formalism for the bending ones. Finally we compare our results with other methods recently proposed in the literature.     

The Coherence Time of Infinite Quantum Well

The relationship among the Coherence time (CT) τ, the Variation frequency λ, the energy separation ΔE and coupling constant α in quantum well was investigated using Pekar type variational method. The results indicated that the Coherence time τ is positively proportional to the Variation frequency λ, but the energy separation ΔE and coupling constant α are negatively correlated with the Coherence time τ. When ΔE is more than 10ev, and when α is more than 5, τ decreases sharply.     

Optical properties and electronic structure of US

The optical properties of uranium sulphide single crystals have been determined for the first time. An excellent agreement is found between the structure in the optical spectrum and the results of a self-consistent cellular multiple scattering calculation. The results evidence that the 5? electrons form a resonance state at E_F and that the 5??6d coupling produces a dip in the 6d density of states near E_F which is responsible for many peculiar properties of US.     

Vertex correction of the anisotropic magnetic impurities to the spin polarization of 2D electron gas

In terms of Kubo's formula and Green's function method, for the two-dimensional electron gas (2DEG) with Rashba spin-orbit coupling (SOC), we study the spin polarization due to the effect from magnetic impurities with anisotropic spin dependent delta type coupling to electrons when an external dc electric field in plane is applied. The vertex correction of impurities in ladder approximation is carried out in the limit of EF?1/τ, Δ. We find that the strength of spin polarization can be significantly modified by vertex correction and the spin polarization is relevant to the anisotropy coefficient γ, but the direction of net spin polarization cannot be changed.     

Motional averaging in an excited state of ZnS: Cu2+

The single isotropic g factor found in the ²E excited state of ZnS:Cu²⁺ is hard to reconcile with the properties of this state, in particular with the moderate strength of the E ? ? vibronic coupling. A vibronic coupling between this state and the vibronic levels of the ground ²T₂ state due to τ₂ modes can bring about motional averaging between strain split states of ²E through a two phonon non-resonant process. In general, excited state mechanisms will be effective between states of the same spin multiplicity and which have large Stoke shifts.     

Fourier-transform microwave spectroscopy of N-methylaniline

The jet-cooled Fourier-transform microwave spectrum of N-methylaniline (C₆H₅-NHCH₃) was recorded in the region of 10-26 GHz, and was analyzed to determine rotational constants and nuclear quadrupole coupling constants. Furthermore, a Coriolis-like coupling parameter characterizing an interaction between an internal rotation of a methyl group and an overall rotation was also determined from A-E splittings observed in pure rotational transitions with high K_a values. The Coriolis-like coupling parameter permitted the determination of the barrier to internal rotation of the methyl group which was found to be 975 cm⁻¹.     

Interplay of valence-shell clusters and the vibrational field in58Ni

The level scheme and electromagnetic properties of⁵⁸Ni are described in the two-particle cluster core coupling model without parameter fitting. The present results are compared to previous shell-model and quasi-particle calculations. To explain the enhancedE2 transitions a neutron effective charge ofe is needed, while the bare value for the vibrator charge has been used.