Electron-phonon coupling with donor-acceptor pair recombination in polar semiconductors

An analysis of the electron-LO phonon interaction function S(R) for donor-acceptor pair transitions in polar semiconductors is presented. Contradicting theoretical results (S is a monotonically increasing function of pair separation distance R, ref. 2) with reliable experimental findings (S needs to be a drecreasing function of R, ref. 5) are removed, if the interaction between LO-phonons and the donor (acceptor) is taken into account more rigorously.     

The kinetics of donor-acceptor pair transitions with strong phonon coupling in GaP

Donor-acceptor pair luminescence in GaP was studied by time-resolved spectroscopy, by measuring and analysing the integral band decay over many decades of intensity and time and by measuring and analysing the temperature dependence of the luminescence intensity. We report here the results obtained with some or all of these techniques for pairs involving deep as well as shallow centres. Those with a deep centre are: S_P-Si_P and Si_Ga-Si_P, in which the acceptor is the deep centre, and O_P-C_P and O_P-Zn_Ga, in which the donor is the deep centre. These pairs all have a broad, phonon-dominated luminescence band. The pairs involving shallow centres include Si_Ga-C_P, S_P-C_P and Te_P-C_P. Due to the different way of momentum conservation in these pairs, those involving a donor on a Ga-site have strong phonon co-operation and weak zero-phonon (ZP) transitions, whereas those with a donor on a P-site have strong ZP transitions.With time-resolved spectroscopy, well-resolved structure, due to a ZP pair band and its phonon replicas, is obtained for nearly all pairs. A comparison is made with the structure obtained by measuring in the stationary state at very low excitation densities. Some trends in the strength of phonon co-operation are noted. In the case of Si_Ga-C_P pairs, sharp replicas of ZP pair lines with a momentum-conserving phonon are also resolved.Using the integral band decay technique and results from time-resolved spectroscopy we have determined the transition probabilities for the total luminescence band as well as for the ZP band for nearly all pairs mentioned. The influence of incomplete saturation of the pairs during excitation with a focussed beam of an argon-ion laser is discussed and approximately corrected for. Extrapolated to zero pair separation, the total transition probability ranges from ∽ 10⁵s^-1 for Si_Ga-C_P pairs to ∽ 15 × 10⁵s^-1 for O_P-C_P and O_P-Zn_Ga pairs. The ZP probability ranges from ∽ 4 × 10³s^-1 for Si_Ga-C_P and Si_Ga-Si_P pairs to ∽ 4 × 10⁵s^-1 for S_P-C_P pairs. The transition probability for pairs in GaP is discussed in relation to the site occupied by the donor and the depth of the centres involved. The relatively high dope concentrations used in some cases, ∽ 1 to 2 × 10¹⁸cm^-3, are discussed briefly in relation to “concentration quenching”.The temperature dependence of the luminescence intensity of S_P-Si_P pairs is satisfactorily analysed with a simple linear model. The same model is applied to similar literature data on the S_P-C_P pair luminescence. Using in addition data on the average pair transition probability, trapping rate constants for hole capture by the Si_P and C_P acceptors were calculated to be ∽ 10^-9 cm³s^-1. Evidence is presented that the trapping rate constant for holes by the Zn_Ga-O_P complex is about 2 × 10^-9 cm³s^-1.     

Critical enhancement of photorefractive beam coupling

We show that a hybridization of the optical and material nonlinearities takes place near the threshold of the subharmonic generation in photorefractive crystals. It results in a critical (with a singularity) enhancement of the rate of spatial amplification of light waves and leads to a variety of new optical critical phenomena.     

Influence of electron-phonon coupling on the energy of an exciton bound to a donor-acceptor pair

The influence of electron-phonon coupling on the binding energy of excitons bound to donor-acceptor pairs is investigated. It is shown that the experimental data in ZnSe agree very well with a theory which takes into account Coulomb overlap and the configuration interaction. The contribution of electron-phonon coupling is small, but not negligible.     

Separation of the exchange and dipolar contributions to the spin-spin coupling in the donor-acceptor complex TAPD-ZnP-NQ

The donor-acceptor complex, 2-tetraalkylphenylenediamine-zinc porphyrin-2-naphthoquinone (TAPD-ZnP-NQ), is studied using transient EPR at K-band (24 GHz). Spin polarized spectra of the radical pair TAPD^+.NQ^?. and of the triplet state TAPD-³ZnP-NQ are observed simultaneously following light excitation of the complex at 30 K in frozen solutions 2-methyl-tetrahydrofuran and the liquid crystal BDH E7. In the liquid crystal, the complex is partially ordered and the spectra depend on the orientation of the sample with respect to the magnetic field. The orientational distribution function is obtained independently by simulating the spectra of the triplet state and assuming that the principal axes of the order matrix coincide with those of the inertia tensor as has been found for solutes in nematic phases. The spectra of TAPD^+.NQ^?. are analyzed on the basis of the coupled correlated radical pair (CCRP) model using an estimate of the geometry based on the X-ray crystal structures of the components and the independently obtained orientational distribution function. It is shown that the experimental spectra are consistent with the assumed geometry and that the exchange coupling,J, is approximately 0.1 mT. This value is at least two order of magnitude larger than that found in the analogous radical pair P^+.Q^?. in photosynthetic reaction centres. This difference is rationalized in terms of different mechanisms for the exchange coupling.     

Experimental determination of the effective strong coupling constant

We present a first attempt to experimentally extract an effective strong coupling constant that we define to be a low Q²$Q^2$ extension of a previous definition by S. Brodsky et al. following an initial work of G. Grunberg. Using Jefferson Lab data and sum rules, we establish its Q²$Q^2$-behavior over the complete Q²$Q^2$-range. The result is compared to effective coupling constants inferred from different processes and to calculations based on Schwinger–Dyson equations, hadron spectroscopy or lattice QCD. Although the connection between the experimentally extracted effective coupling constants and the calculations is not established it is interesting to note that their behaviors are similar.     

Nonperturbative condensate contributions to the effective quark-gluon coupling

We study the effective quark-gluon coupling at low-energy scale, which is defined as the amplitude of a quark emitting or absorbing a gluon with some momentum at low-energy scale. This amplitude is determined from the fermionic three-point Green’s functions of QCD including the leading order contributions of nonperturbative condensates through use of the operator-product expansion. By this approach, we discuss the relationship between the constituent quark and the quark of QCD Lagrangian, and estimate the scale of chiral symmetry breaking and the size of a constituent quark in participating the strong interaction process, such as form factors and radii.     

Vibrational response of hydrogen-bonded interfacial water is dominated by intramolecular coupling

Using the surface-specific vibrational technique of vibrational sum-frequency generation, we reveal that the double-peaked structure in the vibrational spectrum of hydrogen-bonded interfacial water molecules originates from vibrational coupling between the stretch and bending overtone, rather than from structural effects. This is demonstrated by isotopic dilution experiments, which reveal a smooth transition from two peaks to one peak, as D2O is converted into HDO. Our results show that the water interface is structurally more homogeneous than previously thought.     

Universal effective coupling constants for the generalized Heisenberg model

The aim of this study is to find universal critical values of the effective dimensionless coupling constant g ₆ and refined universal values g ₄ for Heisenberg ferromagnets with n-component order parameters. These constants appear in the equation of state and determine the nonlinear susceptibilities χ ₄ and χ ₆ in the critical region. Calculations are made of the first three terms of the expansion of g ₆ in powers of g ₄ in the limits of O(n) symmetry three-dimensional λϕ ⁴ theory, the resultant series is resummed by the Padé-Borel method, and then by substituting the fixed point coordinates g ₄ ^* in the resultant expression, numerical values of g ₆ ^* are obtained for different n. These numbers g ₄ ^* for n>3 were determined from a six-loop expansion for the β-function resummed using the Padé-Borel-Leroy technique. An analysis of the accuracy of these g ₆ ^* values showed that they may differ from the true values by no more than 1.6%. These values of g ₆ ^* were compared with those obtained by the 1/n expansion method which allowed the level of accuracy of this method to be assessed. Fiz. Tverd. Tela (St. Petersburg) 40, 1284–1290 (July 1998)     

Universality of the rho meson coupling in effective field theory

It is shown that both the universal coupling of the rho meson and the Kawarabayashi-Suzuki-Riadzuddin-Fayyazuddin expression for the magnitude of its coupling constant follow from the requirement that chiral perturbation theory of pions, nucleons, and rho mesons is a consistent effective field theory. The prerequisite of the derivation is that all ultraviolet divergences can be absorbed in the redefinition of fields and the available parameters of the most general effective Lagrangian.     

MICE超导耦合磁体线圈等效弹性模量辨识

应用于"μ介子离子化冷却实验装置(MICE)"的超导耦合磁体系统是MICE中的三大关键设备之一。耦合磁体线圈内径为1 500mm,长度为285mm,厚度为110.4mm,采用方形截面1.65×1.00mm2的NbTi复合超导线。每层导线之间为环氧和绝缘玻璃纤维布,每匝导线之间为环氧,线圈具有复杂的正交各向异性性质。根据线圈横截面细观结构的周期性,选出单根导线与周围的绝缘材料为代表性体积元(Representative Volume Element,RVE),基于能量等效原理得出线圈等效弹性模量的含义,然后根据细观力学有限元法,采用有限元软件计算了不同边界条件下细观结构代表性体积元的力学响应,得出了线圈平面径向和环向等效弹性模量,结果已经作为基础数据运用在MICE超导耦合磁体的力学计算中。     

Spin-orbit coupling enhancement of 3d ions in metals

The interactions between localised 3d and itinerant electrons due to the Coulomb and exchange potential are shown to be responsible for the increase in magnitude of ionic spin-orbit coupling.     

The effective potential and the coupling constant at high temperature

The calculation of the effective potential at non-zero temperature is considered. A method of including relevant multi-loop diagrams in the effective potential formalism avoids problems that appear in some earlier treatments. This method is then used to calculate the temperature dependence of the effective coupling constant V⁽⁴⁾ in a scalar λø⁽⁴⁾ theory. The implementation of the renormalization group at high temperature is described, and is used ti show that V⁽⁴⁾ ≈λ/ [1 - (3/16π²)λ ln (T / μ)].     

The effective Hamiltonian for the coupling between inversion-torsion states of hydrazine

In the present paper, a procedure to calculate matrix elements of the group-theoretical Hamiltonian for hydrazine is described and explained in detail, and a complete set of rovibrational matrix elements responsible for interstate interactions is presented. The transformation properties of the framework functions under the symmetry operators of the double group are explained in a simple way using the MS Excel spreadsheet.     

Vibrational spectroscopy of tolane; Coriolis coupling between Raman-active modes of g symmetry

ABSTRACT

Vibrational spectroscopy of tolane (diphenylacetylene), which has 66 normal modes, has been advanced. Anharmonic wavenumber predictions were made with the quartic potential energy surface obtained with B3LYP/cc-pVTZ model and the second-order perturbation theory (VPT2). Infrared (IR) intensity and Raman activities were computed at the harmonic level. The IR spectrum of the crystal and Raman spectra of the liquid and the crystal tolane were newly recorded. The lingering problem of an excess of polarised Raman bands at wavenumbers appropriate for fundamentals, other than a_g modes, has now been attributed to Coriolis coupling within modes of g symmetry species. Consequently, D_2h point symmetry group has been confirmed for a planar tolane molecule. Assignments for almost all fundamentals of tolane are now secure. The assignment for ν₃₂ remains questionable. Remaining unassigned fundamentals are: ν₃₄ and ν₃₅, which, as a_u symmetry species, are IR- and Raman-inactive transitions, and ν₅₉(b_2u), which is predicted to have a very low wavenumber.     

Exact running coupling constants and approximate effective lagrangians

Relations between running coupling constants, which are exact to a number of loops fixed in advance, are derived. The corresponding effective lagrangians are studied, in particular their confining character. Contrary to Adler's conjecture, only the lagrangian corresponding to the one-loop-exact running coupling constant seems to have the desired properties leading to quark confinement.     

Local enhancement of the effective mass near the Fermi surface in nuclear matter

It is shown that the effective mass of nucleons in nuclear matter has a pronounced and narrow maximum near the Fermi surface, in contradistinction with previous belief that this local enhancement exists only in finite nuclei. Implications of this finding for self-consistent Hartree-Fock calculations of finite nuclei are pointed out.