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  • 1
    Electronic Resource
    Electronic Resource
    Coherence and correlation in laser excitation of semiconductor quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1315-1322 
    Details
    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Time resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The concept of coherence due to optical excitation of an ensemble of two-level atoms is relatively simple and well established. For the laser-excited electron-hole pairs or excitions in a semiconductor, the Pauli exclusion and the Coulomb interaction lead to the necessary evolution of the theory of coherence to incorporate the spin degree of freedom, the filling of phase space, the excitons and particularly, their correlation. We have developed two theoretical approaches: one using the Feynman diagrams and one in terms of a force-force correlation function. The former gives us a pictorial way to describe the optical processes and the latter gives us a prescription for computation beyond the perturbative approach. In this paper, we will attempt to use simple physical pictures based on our theory to describe the time development of the coherence, the role of correlation, the dependence on the polarization of light, and the nonlinear time-resolved optical experiments which measure the coherence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457203
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic structure of the light actinide oxides from electron spectroscopy (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3676-3679 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The 4f core level spectra of ThO2, UO2, and NpO2 are shown to be well described in the Anderson impurity model. The O(2p)-actinide (5f ) hybridization is found to be very large. This leads to a new interpretation of the 7-eV satellite in the 4f spectrum, which corresponds to an antibonding 5f n−5f n+1 final state, where n=0,2, and 3 for ThO2, UO2, and NpO2, respectively. The resonance photoemission 4f spectrum is studied, and it is found that interference between different intermediate states is crucial for its interpretation. In particular, the photon energy dependence (CIS spectrum) is strongly influenced by these interference effects. In the 5f valence spectrum of UO2 the theory gives a satellite, which is due to a split-off state caused by the large hybridization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340683
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  • 3
    Electronic Resource
    Electronic Resource
    Systematics in the core level spectra of Th-intermetallics (1986)
    Springer
    The European physical journal 63 (1986), S. 305-311 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the Th 4f core level spectra in a number of related Th-intemetallics, which exhibit interesting trends in terms of the intensity and the energy separation of the satellite with respect to the main signal. With the help of model calculations, we correlate the changes in the core level spectra to the density of states (DOS) in the valence band region. We have studied in detail the effect of changes in the strenght of 5f-conduction band hybridization (Δ), the energy position of the empty 5f level (ε f ) and the DOS in the vicinity ofE F on the spectral shape of Th 4f region. These parameters are also found to affect the binding energies of the main peaks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01303810
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  • 4
    Electronic Resource
    Electronic Resource
    Supersymmetry and Kramers' reaction rate (1990)
    Springer
    The European physical journal 78 (1990), S. 63-67 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In Brinckman's generalization of Kramers' expression for the reaction rate to overcome a high barrier in the large friction limit assumptions about local equilibrium in the wells and the current density at the top of the barrier were made which have been questioned by various authors. It is shown that supersymmetric quantum mechanics can be used to justify Brinckman's result. Exact results for a simple model potential are compared with the asymptotic rate formula.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01317358
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  • 5
    Electronic Resource
    Electronic Resource
    Non-stationary excitonic-insulator states in photoexcited semiconductors (1993)
    Springer
    The European physical journal 91 (1993), S. 189-197 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Time dependent solutions of the semiconductor Bloch equations (SBE) are presented for zero external field which can be identified with a possible dynamics of the so called excitonic-insulator state (EIS) of a semiconductor after the laser pulse has switched off. The collective oscillation of the macroscopic polarization locks into a definite frequency depending on the energy absorbed during the interaction time with the ultra short laser pulse. This dynamical state is different from a stationary EIS proposed previously to be the final state for detunings above the exciton instability and will be demonstrated to appear already for off-resonant excitation. Numerical results are presented for a quasi 1d-model with long-range Coulomb interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01315235
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  • 6
    Electronic Resource
    Electronic Resource
    On the theory of chemisorption (1974)
    Springer
    The European physical journal 267 (1974), S. 201-208 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A solution of the Anderson model for chemisorption including correlation effects is presented. The solution becomes exact in three limiting cases (largeU, smallU i.e. Hartree-Fock and the so-called symmetric strong coupling limit) of the intra atomic Coulomb repulsionU and the hopping termV. Excellent agreement of our approximation with Schrieffer's exact numerical results for the binding energy of a small model system is found. Our results for the binding energy and the charge of the adsorbate show a significant improvement over the Hartree-Fock approximation. The single particle spectral density of the H-F approximation turns out to be even qualitatively wrong in the largeU strong coupling limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01669221
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  • 7
    Electronic Resource
    Electronic Resource
    Luttinger liquids with boundaries: Power-laws and energy scales (2000)
    Springer
    The European physical journal 16 (2000), S. 631-646 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 71.10.-w Theories and models of many electron systems - 71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present a study of the one-particle spectral properties for a variety of models of Luttinger liquids with open boundaries. We first consider the Tomonaga-Luttinger model using bosonization. For weak interactions the boundary exponent of the power-law suppression of the spectral weight close to the chemical potential is dominated by a term linear in the interaction. This motivates us to study the spectral properties also within the Hartree-Fock approximation. It already gives power-law behavior and qualitative agreement with the exact spectral function. For the lattice model of spinless fermions and the Hubbard model we present numerically exact results obtained using the density-matrix renormalization-group algorithm. We show that many aspects of the behavior of the spectral function close to the boundary can again be understood within the Hartree-Fock approximation. For the repulsive Hubbard model with interaction U the spectral weight is enhanced in a large energy range around the chemical potential. At smaller energies a power-law suppression, as predicted by bosonization, sets in. We present an analytical discussion of the crossover and show that for small U it occurs at energies exponentially (in -1/U) close to the chemical potential, i.e. that bosonization only holds on exponentially small energy scales. We show that such a crossover can also be found in other models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510070180
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  • 8
    Electronic Resource
    Electronic Resource
    On correlation effects in the indirect interaction between adatoms (1975)
    Springer
    The European physical journal 22 (1975), S. 143-150 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Starting from a nonorthogonal basis set a model Hamiltonian for the chemisorption of two adsorbates is derived. The nonorthogonality is converted into a renormalization of the matrix elements. A solution is presented which becomes exact in two limiting cases. The indirect interaction energy of two hydrogen atoms is calculated for adsorption on a semi infinite simple cubic solid described by ans-band. For the band nearly filled (parameters of Ni) a 2 × 2 structure seems to be energetically favourable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01322358
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  • 9
    Electronic Resource
    Electronic Resource
    A variational method for hydrogen chemisorption (1975)
    Springer
    The European physical journal 21 (1975), S. 389-392 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Starting from the Hartree-Fock approximation a general variational ansatz for the ground state of the metal-hydrogen system is presented which properly describes the strong correlation effects occuring at larger distances from the surface. As a simple example the Anderson model is studied. The calculated ground state energies are in excellent agreement with exact model calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01325399
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  • 10
    Electronic Resource
    Electronic Resource
    Exactly soluble limits of a model for core level spectra of adsorbates (1978)
    Springer
    The European physical journal 30 (1978), S. 297-303 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photoelectron spectra of core levels for adsorbed atoms or molecules are calculated for a model which allows the screening of the core hole both by coupling to the surface plasmons and by charge transfer to the adsorbate. Exact analytical expressions for the core spectra are given for the case where the charge transfer occurs from a filled substrate band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320035
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