Coherent Features of Resonance-Mediated Two-Photon Absorption Enhancement by Varying the Energy Level Structure,Laser Spectrum Bandwidth and Central Frequency

The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light-matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited(TL)-normalized final state population maximun. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.     

Semiempirical model calculations for chemisorption on transition metals: III. CO,N2 and NO on Ni,Cu, Pd and Ag

An effective one electron Hamiltonian is used to calculate the qualitative behaviour of various physical quantities (adsorption energy, shifts of ionization energies, energy profiles, etc.) over a series of different adsorption systems. The numerical calculations allow for several orbitals on the adsorbed particle as well as for the s- and the d-and in the metal. The experimentally found trends concerning the general features of photoelectron spectra and the variation of the adsorption energy with adsorbate and substrate as well as with the surface orientation and the location of the adsorbed species are reproduced reasonably well. A simple theory of photoemission (the final state is a plane wave) has been combined with the semiempirical calculations. The generally observed decrease of emission from the d-band region can be understood as an interference effect in the initial state.     

Fluorescence quantum yields and lifetimes of H- (-CC-)-2X+, X-(-CC-)-2 X2 and CH3 -(-C  C-)-n X+, n = 1, 2, with X = Cl,Br, in their à states

A photoelectron—photon coincidence technique has been used to determine fluorescence quantum yields and lifetimes of the state-selected cations given in the title. The data, obtained under collision-free conditions, yield the radiative and non-radiative rate constants as functions of the internal energy in the excited state. The essential features of the results are discussed briefly and some of the observations made in related spectroscopic studies are explained.     

Mechanisms of modification of the energy spectrum in high-temperature superconductors of the bismuth,thallium, and mercury systems upon doping and increase in the number of copper-oxygen layers

This paper reports on the results of a comparative investigation of the specific features of the electron transport and superconducting properties in chain-free high-temperature superconductors of the bismuth, thallium, and mercury systems with different levels and types of doping, as well as with different numbers of copper-oxygen layers. It has been shown that the asymmetric narrow band model provides a means for adequately describing the available data on temperature dependences of the thermopower coefficient for all the studied systems, which has proved the possibility of applying this model as a universal method for describing and analyzing the specific features of the electron transport in high-temperature superconductors of different systems. The parameters of the energy spectrum and the system of charge carriers in the normal phase have been determined, and the general regularities in the transformation of the energy spectrum due to the doping and an increase in the number of copper-oxygen layers in different systems have been revealed. The conclusions have been drawn about the character and mechanisms of influence of the parameters of the energy spectrum in the normal state on the superconducting properties of chain-free high-temperature superconductors in the optimally doped and underdoped regimes. It has been demonstrated that, in the underdoped regime, regardless of the type of doping, the dependence of the critical temperature on the effective width of the conduction band has a close-to-universal character in all the studied systems for each of the phases with different numbers of copper-oxygen layers.     

Linear expansion, phase separation, and magnetic inhomogeneities in La0.92Ca0.08MnO3

A relation of the thermal expansion with magnetic and magnetotransport properties has been revealed in La_0.92Ca_0.08MnO₃ single crystals in the paramagnetic state. The magnetotransport and lattice properties and the specific features in the neutron scattering characteristics of the La_0.92Ca_0.08MnO₃ single crystals have been explained by the phase separation in the paramagnetic state into magnetic inhomogeneities (clusters) with short-range (～10 Å) and long-range (>10² Å) orders. The performed investigations have demonstrated that the clusters are closely related to the crystal lattice and that the magnetic inhomogeneities in the paramagnetic region are correlated to T ～ 250–300 K ? TC.     

Resonance features of the dynamic magnetic susceptibility in hexaferrite BaFe12O19 upon the transition from the magnetically ordered state to the paramagnetic state

This paper presents the results of the experimental study on the dynamic magnetic susceptibility of barium hexaferrite crystals in the temperature range of the transition from the magnetically ordered state to the paramagnetic state. The observed features of the magnetic susceptibility have been interpreted as those characteristic of the ultralow-frequency natural ferromagnetic resonance of the spin subsystem of the Bloch domain walls. The results agree well with the concepts of features of the critical spin dynamics near the Curie temperature.     

Dynamics of Entropy and Nonclassicality Features of the Interaction between a ◊-type Four-Level Atom and a Single-Mode Field in the Presence of Intensity-Dependent Coupling and Kerr Nonlinearity

The interaction between a ◊-type four-level atom and a single-mode field in the presence of Kerr medium with intensity-dependent coupling involving multi-photon processes has been studied. Using the generalized (nonlinear) Jaynes-Cummings model, the exact analytical solution of the wave function for the considered system under particular condition, has been obtained when the atom is initially excited to the topmost level and the field is in a coherent state. Some physical properties of the atom-field entangled state such as linear entropy showing the entanglement degree, Mandel parameter, mean photon number and normal squeezing of the resultant state have been calculated. The effects of Kerr medium, detuning and the intensity-dependent coupling on the temporal behavior of the latter mentioned nonclassical properties have been investigated. It is shown that by appropriately choosing the evolved parameters in the interaction process, each of the above nonclassicality features, which are of special interest in quantum optics as well as quantum information processing, can be revealed.     

Peculiarities of the rotational dynamics of an ensemble of diatomic homonuclear molecules in a strong laser field

The rotational dynamics of an ensemble of molecules in a laser field has been studied. The results obtained within the framework of the quantum-mechanical and classical approaches have been compared. The features of the rotational dynamics connected with the non-classical character of the system have been described. It was taken into account that before the interaction with a laser pulse the ensemble was in a thermodynamically equilibrium mixed state. The case of an ultrashort laser pulse has been considered as well.     

Change in surface states of Ag(111) thin films upon adsorption of a monolayer of PTCDA organic molecules

The change in the electronic structure of silver thin films of different thicknesses with the Ag( 111) orientation due to the interaction with an adsorbed monolayer of ordered organic molecules of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) has been investigated in terms of density functional theory. It has been shown that one of the two surface states of the pure films transforms into an unocc upied interface state due to the interaction so that all the main features of the initial state are retained. The relation of the resulting state to the unoccupied state experimentally observed in the PTCDA/Ag( 111 ) system by scanning tunneling and two-photon photoemi ssion spectroscopy has been discussed.     

Dynamic conductivity modified by impurity resonant states in doping three-dimensional Dirac semimetals

The impurity effect is studied in three-dimensional Dirac semimetals in the framework of a T-matrix method to consider the multiple scattering events of Dirac electrons off impurities. It has been found that a strong impurity potential can significantly restructure the energy dispersion and the density of states of Dirac electrons. An impurity-induced resonant state emerges and significantly modifies the pristine optical response. It is shown that the impurity state disturbs the common longitudinal optical conductivity by creating either an optical conductivity peak or double absorption jumps, depending on the relative position of the impurity band and the Fermi level. More importantly, these conductivity features appear in the forbidden region between the Drude and interband transition, completely or partially filling the Pauli block region of optical response. The underlying physics is that the appearance of resonance states as well as the broadening of the bands leads to a more complicated selection rule for the optical transitions, making it possible to excite new electron-hole pairs in the forbidden region. These features in optical conductivity provide valuable information to understand the impurity behaviors in 3D Dirac materials.     

Pore- and delamination-induced mismatch strain relaxation and conditions for the formation of dislocations,cracks, and buckles in the epitaxial AlN(0001)/SiC/Si(111) heterostructure

A method has been proposed using the example of an AlN/SiC/Si heterostructure according to which the strain state induced in multilayer epitaxial films by the mismatch in the lattice parameters and thermal expansion coefficients of the crystals can be calculated from the experimental temperature dependence of the curvature of the crystal plate. The method makes it possible to estimate the imperfection of the hetero-structure from defect-relieved mechanical stresses caused by mismatch strains. It has been found that there are specific features in the formation of the relief of AlN films grown on SiC/Si substrates prepared by the atomic substitution. Criteria for the formation and preferred orientations of defects (dislocations, cracks, delaminations, and buckles) in AlN films have been calculated. For this purpose, the surface energies and energies of adhesion for different twins at the semiconductor interfaces have been calculated using computational quantum chemistry methods for different crystal faces.     

A theoretical study on the excited states of MC3 (M = Sc, V, and Cr)

The ground state structures of MC₃ (M = Sc, V, and Cr) and their anions have been investigated, employing the first-principles DFT at the B3LYP level. The calculations predict that the equilibrium geometries of both neutral MC₃ and their anions are cyclic structures with C_2v symmetry. The Mulliken charge and spin populations of MC₃ and their anions have also been calculated, and it is found the electron charge changes mainly take place on the M atoms from anions to neutral molecules. The low-lying excited states for the clusters are calculated with time-dependent DFT to assign the features of the photoelectron spectra. Our results agree well with the available experimental and theoretical data.     

Decoherence,the Density Matrix,the Thermal State and the Classical World

Decoherence has been the basis for understanding the emergence of the classical world from its quantum underpinnings. Unfortunately the calculations establishing decoherence overshoot and, based on assumptions that break down, predict that with the passage of time the off-diagonal elements of the density matrix become arbitrarily small. It has been recognized by some authors that the thermal state, assumed to hold for systems in equilibrium, places a bound on off diagonal terms. In this article we establish—preserving the conservation of energy, as is not the case for previous work—that indeed the thermal state is an attractor under scattering. Moreover, the bound on the off-diagonal terms present in the thermal state does not contradict everyday experience.     

Measuring the similarity between trajectories using clustering techniques

A clustering method has been developed to group signals that display similar dynamic behavior. The procedure involves using the method of time delay embedding to construct a trajectory in state space from a time series. Certain features that characterize the geometry of the trajectory have been defined. These features were subjected to a series of statistical tests to determine their usefulness in a hierarchical clustering analysis. The latter is aimed at finding groups of similar trajectories. The trajectory-based clustering algorithm has been applied to simulated data, which included both stochastic data generated by a linear AR model, and nonlinear data generated by a Duffing oscillator. The results show that the algorithm works reliably in both cases.     

An alternative method for spectrum of a two-electron-quantum dot

The subject of quantum dot has received great theoretical attention because of many attractive features they exhibit in a large class of combinations and different methods have been used. In the present work, we consider a two-electron-quantum dot, obtain the quasi-exact analytical solution of corresponding Schrödinger equation and finally calculate the ground state and the excited state energy eigenvalues of the system by considering oscillating and linear confining terms as well as a Coulomb interaction between the two electrons. The present results are useful to study the optical and magnetic properties of such structures.     

Fluorescence spectrum characteristic of ethanol--water excimer and mechanism of resonance energy transfer

The steady-state fluorescence spectrum characteristic of ethanol--water excimer has been studied in this paper. By analysing the features of the sharp emission spectrum with fine structures in a shortwave band and the characteristics of the broad and featureless fluorescence peaks in the longwave band, one can conclude that the excimers are formed between the new ethanol--water cluster molecules in the excited state and the ground state through the interaction among different chromophores. The excitation spectra in the two fluorescence bands have been studied, and their emission mechanisms have been ascertained based on the energy transfer theory. Furthermore, the critical distance of the resonance energy transfer has been calculated.     

Hyperpolarized long-lived states in solution NMR: three-spin case study in low field

Recent work has shown that singlet states in two-spin systems can possess lifetimes exceeding the T(1) relaxation time, provided that the system is kept under conditions that minimize the effects of the chemical shift Hamiltonian (for instance under low magnetic field or RF irradiation). Similar observations have been made in hyperpolarized states of multi-spin systems prepared via parahydrogen-induced polarization (PHIP). However, lifetime prolongation mechanisms in multi-spin systems are still under investigation. Here we present experimental observations of a long-lived state in a three-spin system prepared by PHIP and stored at low field. The observed lifetime of the long-lived state is 144s, about twice as long as the longest T(1) measured in the system at high field. The results are analyzed using a recently proposed theory of lifetime prolongation in multi-spin systems in low field. It is shown that quantum mechanical selection rules governing intramolecular dipolar relaxation in low field account for the enhanced lifetime and spectral features of this state.     

A conversion electron Mössbauer spectroscopy study of ion beam mixing at Fe: Polyethylene interface

The effects of ion beam induced atomic mixing at the Fe-Polyethylene interface have been investigated by means of conversion electron Mössbauer spectroscopy [CEMS]. It is shown that the as deposited and ion beam mixed composites exhibit distinctly different features. In particular, the ion beam mixed composite shows that presence of Fe²⁺ state in polyethylene matrix along with the Fe?C austenite like phase.     

Polaron effects on superexchange interaction: Isotope shifts of T N , T c , and T* in layered copper oxides

A compact expression has been obtained for the superexchange coupling of magnetic ions via intermediate anions with regard to polaron effects on both magnetic ions and intermediate anions. This expression is used to analyze the main features of the behavior of isotope shifts for temperatures of three types in layered cuprates: the Neel temperatures (T _N ), critical temperatures of transitions to a superconducting state (T _c ), and characteristic temperatures of the pseudogap state of normal phases (T*).