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Jonak-Auer, I.; Meisels, R.; Kuchar, F.; McCombe, B.D.

46th annual symposium of the Austrian Physical Society. Programme and abstracts1996

46th annual symposium of the Austrian Physical Society. Programme and abstracts1996

AbstractAbstract

No abstract available

Original Title

Magnetfeldinduzierte Aenderung des Ladungstraegertyps in (111)-InGaAs/GaAs Uebergittern

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Schindler, H.G. (ed.); Oesterreichische Physikalische Gesellschaft, Vienna (Austria); 218 p; 1996; p. 18; 46. annual symposium of the Austrian Physical Society; 46. Jahrestagung der Oesterreichischen Physikalischen Gesellschaft; Linz (Austria); 23-27 Sep 1996

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Miscellaneous

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Arko, A.J.; Joyce, J.J.; Sarrao, J.; Thompson, J.D.; Morales, L.; Fisk, Z.; Henkie, Z.; Cichorek, T.

Los Alamos National Lab., NM (United States). Funding organisation: USDOE Office of Energy Research, Washington, DC (United States); National Science Foundation, Washington, DC (United States)1998

Los Alamos National Lab., NM (United States). Funding organisation: USDOE Office of Energy Research, Washington, DC (United States); National Science Foundation, Washington, DC (United States)1998

AbstractAbstract

[en] The term heavy fermions refers to materials (thus far only compounds with elements having an unfilled 4f or 5f shells) whose large specific heat γ-values suggest that the conduction electrons at low temperatures have a very heavy effective mass. Magnetic susceptibility measurements, χ, generally yield a Curie-Weiss behavior at high temperatures with a well developed moment, which would be consistent with localized behavior of the f-electrons. Thus, the f-electrons appear to behave as non-interacting single impurities at elevated temperature. Below a characteristic Kondo temperature, T

_{K}, the susceptibility levels off or even decreases. This is interpreted as a compensation of the f-moment by the ligand conduction electrons that are believed to align anti-parallel to form a singlet state and has led to the widespread use of the Anderson Impurity Hamiltonian and the Single Impurity Model (SIM). Weak hybridization with these conduction electrons yields a narrow, highly temperature dependent, DOS at the Fermi energy, often referred to as the Kondo resonance (KR). At still lower temperatures it is generally agreed that in stoichiometric compounds a lattice of these singlet states finally results in extremely narrow bands at the Fermi energy, whose bandwidth is of the order k_{B}T_{K}. Clearly coherent bands cannot form above T_{K}owing to the narrow width. A model for periodic Kondo systems will inevitably have to include the lattice. Preliminary PAM calculations indicate that this inclusion yields results differing qualitatively, rather than just quantitatively, from the SIM predictions. The photoemission data on single crystal heavy fermions are consistent with the following PAM predictions: (1) the temperature dependence of the KR is much slower than expected from the SIM; indeed, it is primarily7 due to broadening and Fermi function truncation; (2) the spectral weight of the KR relative to the localized 4f feature (not discussed here) is much larger than the SIM expectations (equivalently, n_{f}values are far too small); (3) the KR and its sidebands does not lose spectral weight with T, but rather only broadens; (4) f-electrons in both Ce and U systems form narrow bands already far above T_{K}(the jury is still out for Yb systems); (5) the width of these bands is much larger than k_{B}T_{K}; (6) f-character is obtained in only some regions of the Brillouin zone; i.e., momentum dependence of the KR above T_{K}. While the PAM seems to predict the correct trends, they have no reason yet to rule out other models, such as those of Liu and Sheng and Cooper. Such discrimination may occur when the models develop sufficiently to allow real system calculationsPrimary Subject

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1998; 7 p; Euroconference on polarons: condensation, pairing, magnetism; Erice (Italy); 9-17 Jun 1998; CONF-9806129--; CONTRACT W-7405-ENG-36; AWARD NSF DMR-95-31009; ALSO AVAILABLE FROM OSTI AS DE99001226; NTIS; INIS; US GOVT. PRINTING OFFICE DEP

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[en] Configuration-interaction calculations with Breit-Pauli relativistic corrections have been carried out for aluminum ions for the purpose of studying Kα satellite spectra obtained during intense proton-beam--plasma interaction experiments. We present results for calculated wavelengths, oscillator strengths, and fluorescence yields of Kα satellites for Al I--Al XI . Detailed calculations have been performed both for transitions involving levels of ground-state configurations and for transitions involving levels of low-lying excited configurations with M-shell spectator electrons. Calculated wavelengths for the Kα transitions are compared with a spectrum obtained during a Particle Beam Fusion Accelerator II proton-beam experiment [Lasers Part. Beams 8, 555 (1990)] at Sandia National Laboratories. Our calculations show that the Kα satellite lines of aluminum ions can be classified into two distinct groups: one involving transitions of type 1s

^{1}2s^{r}2p^{q}→1s^{2}2s^{r}2p^{q-1}, the other 1s^{1}2s^{r}2p^{q-1}3l→1s^{2}2s^{r}2p^{q-2}3l. The former consists of the resonance Kα transitions, which gives the characteristic satellite-line position of an ion, while the latter overlaps with the resonance Kα lines of the next-higher ionization stage. We find that both correlation effects and relativistic corrections significantly impact the calculated Kα transition energiesPrimary Subject

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Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics; ISSN 1063-651X; ; CODEN PLEEE8; v. 48(5); p. 3934-3942

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[en] The Schroedinger equation with a classical electrostatic potential is used to describe the Rydberg states of an electron moving near a spherical metal surface. An exact solution is obtained for a discrete sequence of sphere radii. As the sphere radius goes to infinity, the discrete spectrum coincides with the known spectrum derived for a plane metal-vacuum interface. Knowing the dependence of the Rydberg state energy on the sphere radius, one can evaluate these radii from experimental data. 5 refs., 1 fig., 1 tab

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Cover-to-cover Translation of Optika i Spektroskopiya (USSR); Translated from Optika i Spektroskopiya; 73: No. 1, 48-54(Jul 1992).

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Numerical Data; Translation

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[en] The authors have determined the dynamic dipole (α

_{1}), quadrupole (α_{3}), and dipole-dipole-quadrupole (B) polarizabilities and the second hyperpolarizability tensor (γ) for the helium atom in its lowest triplet state (2^{3}S). They have done so for both real and imaginary frequencies: in the former case, for a range of frequencies (ω) between zero and the first electronic-transition frequency, and in the latter case for a 32-point Gauss-Legendre grid running from zero to ℎω = 20 E_{h}. They have also determined the dispersion-energy coefficients C_{6}, C_{8}, and C_{10}for the systems H(1^{2}S)-He(2^{3}X), He(1^{1}S)-He(2^{3}S), and He(2^{3}S)-He(2^{3}S) and the C_{6}^{0}, C_{6}^{2}, C_{8}^{0}, C_{8}^{4}coefficients for the interaction He(2^{3}S)-H_{2}(X^{1}Σ_{g}^{+}). Their values of the higher-order multipolar polarizabilities and of γ for the 2^{3}S state of helium are, they believe, the first to be published. 14 refs., 5 tabsPrimary Subject

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[en] A qualitative description is given of configuration degeneracy in the vibrational-rotational spectrum of a nonrigid molecule. Using the NH

_{3}molecule in a nondegenerate vibrational state as an example, this description is shown to be strongly dependent on the type of transition between energetically equivalent equilibrium configurations. For a nonpermutation transition observed in this molecule, a procedure is proposed for a qualitative construction of an effective configurational-rotational Hamiltonian as well as of generators of its transformation into a reduced form. 12 refs., 1 fig., 1 tabPrimary Subject

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Cover-to-cover Translation of Optika i Spektroskopiya (USSR); Translated from Optika i Spektroskopiya; 73: No. 4, 702-707(Oct 1992).

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Translation

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[en] We have studied two different systems producing resonances, a highly excited multielectron Coulombic negative ion (the He

^{-}2s2p^{2}^{4}P state) and a hydrogen atom in a magnetic field, via the complex-coordinate rotation (CCR) and the state-specific complex-eigenvalue Schroedinger equation (CESE) approaches. For the He^{-}2s2p^{2}^{4}P resonance, a series of large CCR calculations, up to 353 basis functions with explicit r_{ij}dependence, were carried out to serve as benchmarks. For the magnetic-field problem, the CCR results were taken from the literature. Comparison shows that the state-specific CESE theory allows the physics of the problem to be incorporated systematically while keeping the overall size of the computation tractable regardless of the number of electronsPrimary Subject

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[en] We have used a first-principles, density-functional-based method to calculate the electric polarizabilities and dipole moments for several low-energy geometries of Si clusters in the size range 10≤N≤20. The polarizability per atom is found to be a slowly varying, nonmonotonic function of N. Over this size range the polarizability appears to be correlated most strongly to cluster shape and not with either the dipole moment or the highest occupied - lowest unoccupied molecular-orbital gap. The calculations indicate that the polarizability per atom for Si clusters approaches the bulk limit from above as a function of size. copyright 1999 The American Physical Society

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[en] Adapting an approach used by Feynman for the Lamb shift of an isolated atom, we obtain a nonperturbative expression for the Lamb shift of an atom in a dielectric medium, previously calculated perturbatively [P. W. Milonni, J. Mod. Opt. 42, 1191 (1995)]. The separation of the Lamb and Casimir components of the field energy is greatly simplified, and previous nonperturbative results for the Lamb shift [M. Schaden, L. Spruch, and F. Zhou, Phys. Rev. A 57, 1108 (1998)], based on the generalized argument theorem, are obtained much more easily and directly. copyright 1999 The American Physical Society

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[en] We present polaron effective masses and selected polaron band structures of the Holstein molecular crystal model in one dimension as computed by the Global-Local variational method over a wide range of parameters. These results are augmented and supported by leading orders of both weak- and strong-coupling perturbation theory. The description of the polaron effective mass and polaron band distortion that emerges from this work is comprehensive, spanning weak, intermediate, and strong electron-phonon coupling, and nonadiabatic, weakly adiabatic, and strongly adiabatic regimes. Using the effective mass as the primary criterion, the self-trapping transition is precisely defined and located. Using related band-shape criteria at the Brillouin-zone edge, the onset of band narrowing is also precisely defined and located. These two lines divide the polaron parameter space into three regimes of distinct polaron structure, essentially constituting a polaron phase diagram. Though the self-trapping transition is thus shown to be a broad and smooth phenomenon at finite parameter values, consistency with the notion of self-trapping as a critical phenomenon in the adiabatic limit is demonstrated. Generalizations to higher dimensions are considered, and resolutions of apparent conflicts with well-known expectations of adiabatic theory are suggested. copyright 1999 The American Physical Society

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