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  • 2000-2004  (6)
  • 1970-1974
  • 1965-1969
  • 1890-1899
  • 1800-1809
  • 2001  (6)
  • PACS. 03.75.Fi Phase coherent atomic ensembles; quantum condensation phenomena – 05.30.Jp Boson systems – 32.80.Pj Optical cooling of atoms; trapping  (2)
  • PACS. 32.80.Pj Optical cooling of atoms; trapping – 42.50.Vk Mechanical effects of light on atoms, molecules, electrons, and ions  (2)
  • PACS. 61.12.-q Neutron diffraction and scattering – 61.66.Fn Inorganic compounds – 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.) – 75.30.Et Exchange and superexchange interactions  (2)
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  • 2000-2004  (6)
  • 1970-1974
  • 1965-1969
  • 1890-1899
  • 1800-1809
Year
Keywords
  • 1
    Electronic Resource
    Electronic Resource
    Crystal and magnetic structures of the oxyphosphates MFePO 5 (M = Fe, Co, Ni, Cu). Analysis of the magnetic ground state in terms of superexchange interactions (2001)
    Springer
    The European physical journal 22 (2001), S. 429-442 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 61.12.-q Neutron diffraction and scattering – 61.66.Fn Inorganic compounds – 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.) – 75.30.Et Exchange and superexchange interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We have studied in detail the crystal and magnetic structures of the oxyphosphates MFePO5 (M: divalent transition metal) using neutron powder diffraction as a function of temperature. All of them are isomorphic to the mixed valence compound α-Fe2PO5 with space-group Pnma. No disorder exists between the two metallic sites. The M2+O6 octahedra share edges between them and faces with Fe3+O6 octahedra building zigzag chains running parallel to the b-axis that are connected by PO4 tetrahedra. The topology of this structure gives rise to a complex pattern of super-exchange interactions responsible of the observed antiferromagnetic order. The magnetic structures are all collinear with the spin directed along the b-axis except for M = Co. The experimental magnetic moments of Cu+2 and Ni2+ correspond to the expected ionic value, on the contrary the magnetic moment of Fe3+ is reduced, probably due to covalence effects, and that of Co2+ is greater than the spin-only value indicating a non negligible orbital contribution. Using numerical calculations we have established a magnetic phase diagram adapted for this type of crystal structure and determined the constraints to be satisfied by the values of the exchange interactions in order to obtain the observed magnetic structure as the ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510170093
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  • 2
    Electronic Resource
    Electronic Resource
    Neutron diffraction study of the magnetic ordering in the series R 2 BaNiO 5 (R = Rare Earth) (2001)
    Springer
    The European physical journal 24 (2001), S. 59-70 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 61.12.-q Neutron diffraction and scattering – 61.66.Fn Inorganic compounds – 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.) – 75.30.Et Exchange and superexchange interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: A neutron diffraction study, as a function of temperature, of the title compounds is presented. The whole family (space group Immm, a ≈ 3.8Å, b ≈ 5.8Å, c ≈ 11.3Å) is structurally characterised by the presence of flattened NiO6 octahedra that form chains along the a-axis, giving rise to a strong Ni-O-Ni antiferromagnetic interaction. Whereas for Y-compound only strong 1D correlations exist above 1.5 K, presenting the Haldane gap characteristic of 1D AF chain with integer spin, 3D AF ordering is established simultaneously for both R and Ni sublattices at temperatures depending on the rare earth size and magnetic moment. The magnetic structures of R2BaNiO5 ( R = Nd, Tb, Dy, Ho, Er and Tm) have been determined and refined as a function of temperature. The whole family orders with a magnetic structure characterised by the temperature-independent propagation vector = (1/2, 0, 1/2). At 1.5 K the directions of the magnetic moments differ because of the different anisotropy of the rare earth ions. Except for Tm and Yb (which does not order above 1.5 K), the magnetic moment of the R3+ cations are close to the free-ion value. The magnetic moment of Ni2+ is around 1.4 , the strong reduction with respect to the free-ion value is probably due to a combination of low-dimensional quantum effects and covalency. The thermal evolution of the magnetic structures from T N down to 1.5 K is studied in detail. A smooth re-orientation, governed by the magnetic anisotropy of R3+, seems to occur below and very close to T N in some of these compounds: the Ni moment rotates from nearly parallel to the a-axis toward the c-axis following the R moments. We demonstrate that for setting up the 3D magnetic ordering the R-R exchange interactions cannot be neglected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510170022
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  • 3
    Electronic Resource
    Electronic Resource
    Coherent control of the self-trapping transition (2001)
    Springer
    The European physical journal 20 (2001), S. 451-467 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 03.75.Fi Phase coherent atomic ensembles; quantum condensation phenomena – 05.30.Jp Boson systems – 32.80.Pj Optical cooling of atoms; trapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We discuss the dynamics of two weakly coupled Bose-Einstein condensates in a double-well potential, contrasting the mean-field picture to the exact N-particle evolution. On the mean-field level, a self-trapping transition occurs when the scaled interaction strength exceeds a critical value; this transition essentially persists in small condensates comprising about 1000 atoms. When the double-well is modulated periodically in time, Floquet-type solutions to the nonlinear Schrödinger equation take over the role of the stationary mean-field states. These nonlinear Floquet states can be classified as “unbalanced” or “balanced”, depending on whether or not they entail long-time confinement of most particles to one well. Since the emergence of unbalanced Floquet states depends on the amplitude and frequency of the modulating force, we predict that the onset of self-trapping can efficiently be controlled by varying these parameters. This prediction is verified numerically by both mean-field and N-particle calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00011106
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Instanton approach to Josephson tunneling between trapped condensates (2001)
    Springer
    The European physical journal 17 (2001), S. 351-363 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 03.75.Fi Phase coherent atomic ensembles; quantum condensation phenomena – 05.30.Jp Boson systems – 32.80.Pj Optical cooling of atoms; trapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: An instanton method is proposed to investigate the quantum tunneling between two weakly-linked Bose-Einstein condensates confined in double-well potential traps. We point out some intrinsic pathologies in the earlier treatments of other authors and make an effort to go beyond these very simple zero order models. The tunneling amplitude may be calculated in the Thomas-Fermi approximation and beyond it; we find it depends on the number of the trapped atoms, through the chemical potential. Some suggestions are given for the observation of the Josephson oscillation and the MQST.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530170010
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Single-beam optical bottle for cold atoms using a conical lens (2001)
    Springer
    The European physical journal 14 (2001), S. 373-376 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Pj Optical cooling of atoms; trapping – 42.50.Vk Mechanical effects of light on atoms, molecules, electrons, and ions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We report a new method to generate an optical dipole potential with a null intensity region surrounded in all directions by light walls. This is achieved with a simple scheme based on a conical lens. Applications to optical trapping of neutral atoms are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530170205
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    A continuous cold atomic beam from a magneto-optical trap (2001)
    Springer
    The European physical journal 15 (2001), S. 245-249 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Pj Optical cooling of atoms; trapping – 42.50.Vk Mechanical effects of light on atoms, molecules, electrons, and ions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We have developed and characterized a new method to produce a continuous beam of cold atoms from a standard vapour-cell magneto-optical trap (MOT). The experimental apparatus is very simple. Using a single laser beam it is possible to hollow out in the source MOT a direction of unbalanced radiation pressure along which cold atoms can be accelerated out of the trap. The transverse cooling process that takes place during the extraction reduces the beam divergence. The atomic beam is used to load a magneto-optical trap operating in an ultra-high vacuum environment. At a vapour pressure of 10-8mbar in the loading cell, we have produced a continuous flux of 7×107atoms/s at the recapture cell with a mean velocity of 14 m/s. A comparison of this method with a pulsed transfer scheme is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530170172
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