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  • 1
    Electronic Resource
    Electronic Resource
    Systematic improvement of variational Monte Carlo using Lanczos iterations (1993)
    Springer
    The European physical journal 90 (1993), S. 73-77 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a new numerical technique which combines the variational Monte Carlo and the Lanczos methods without suffering from the fermion sign problem. Lanczos iterations allow systematic improvement of trial wavefunctions while Monte Carlo sampling permits treatment of large lattices. As in the usual Lanczos method we find it useful to symmetrize the starting wavefunction in order to accelerate convergence. We apply our method to the 2D AFM Heisenberg model in the fermionic electron representation, which allows us to compare with results from the equivalent bosonic spin representation. Using d-wave RVB states as starting wavefunctions shows that after only one iteration between 70 and 80% of the difference between the variational energy and the ground state energy (as determined by GFMC) is recovered, and a similar improvement is observed in the second iteration. Leaving the spin-singlet sector by introducing antiferromagnetic correlations reduces the symmetry and the relative improvement in energy drops below 50% for one iteration. Our method allows us also to see trends in observables. Relative to the d-wave RVB states we find an enhancement in the spinspin correlations, consistent with the expectation that the true ground state has long-range order.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01321035
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  • 2
    Electronic Resource
    Electronic Resource
    A touchstone for theories (1989)
    [s.l.] : Nature Publishing Group
    Nature 337 (1989), S. 686-687 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE observation by Tranquada et al., reported on page 720 of this issue1, of singly charged copper ions in the superconductor Nd2_^Ce^CuO4 confirms the suggestion made in Nature last month by Tokura and co-workers2 that this material is an electron-doped high-temperature cuprate superconductor. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/337686a0
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  • 3
    Electronic Resource
    Electronic Resource
    Clues from copper-free samples (1988)
    [s.l.] : Nature Publishing Group
    Nature 332 (1988), S. 780-780 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ALTHOUGH the superconducting transition temperature (jTc) of the compound Ba,_,Kx BiO3 reported by Cava et al. on page 814 of this issue1 is, at 30 K, much less than others reported over the past year (see figure), it is substantially higher than the highest value (23 K) obtained previously in ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/332780a0
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  • 4
    Electronic Resource
    Electronic Resource
    Heavy-electron metals (1986)
    [s.l.] : Nature Publishing Group
    Nature 320 (1986), S. 124-129 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A new class of metals has been found in which the electrons have effective masses orders of magnitude larger than the free-electron mass. Some of these metals are superconducting at low temperatures. This superconductivity seems to be unconventional, with an underlying mechanism different from that ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/320124a0
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetic properties Ferromagnetism in the hexaborides (1999)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 402 (1999), S. 251-253 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The cubic hexaborides of the rare-earth elements have a wide variety of physical properties, despite their simple crystallographic structures. For example, the ‘doped’ hexaboride Ca1−xLaxB6 is ferromagnetic, even though it has no partially ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/46207
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  • 6
    Electronic Resource
    Electronic Resource
    d-Wave superconductivity in thet-J model using a systematically improved Variational Monte Carlo method (1995)
    Springer
    Journal of low temperature physics 99 (1995), S. 557-559 
    Details
    ISSN: 1573-7357
    Keywords: 71.10 ; 74−70V ; 74−20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We can construct unbiased systematic improvements of standard Variational Monte Carlo calculations by the use of wavefunctions modified by short range operators. Using the energy and spectral width of the original and improved wavefunctions we can judge the quality of the trial wavefunctions. For the t-J model we find the regions of phase separation and d-wave superconductivity with varying J/t and hole density S and extend the T=0 phase diagram into the physically interesting region of δ ∼ 0.1 – 0.2and J/t ∼ 0.4.Above the critical ratio of J/t¦ c we find clear evidence of dx2-y2-pairing and above a higher value J/t¦s phase separation. At δ=0.16we obtain values J/t¦ c=0.4and J/t¦ s=0.7. Cluster sizes up to 50 sites are used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00752340
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  • 7
    Electronic Resource
    Electronic Resource
    Crossover from Fermi liquid to classical behavior of normal3He in the model of almost localized fermions (1986)
    Springer
    Journal of low temperature physics 64 (1986), S. 195-221 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A phenomenological extension of the model of almost localized fermions to finite temperatures is presented. It is used to calculate thermodynamic properties of the normal state of3He. No new adjustable parameters are introduced and the effective interaction strength is the same as used by Vollhardt. A good qualitative description of the crossover from Fermi liquid to classical behavior in the specific heat, spin susceptibility, and temperature-dependent pressure (or equivalently thermal expansion) is obtained. In particular, key results, such as the change in specific heat when the spin entropy saturates and the change from thermal expansion to thermal contraction at low temperatures are reproduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00685129
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  • 8
    Electronic Resource
    Electronic Resource
    Cuprates intermediate between one and two dimensions (1994)
    Springer
    Journal of low temperature physics 95 (1994), S. 299-308 
    Details
    ISSN: 1573-7357
    Keywords: 75.10 ; 74.20 ; 74.72
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The key elements in all known cuprate superconductors are lightly doped CuOi-planes. Recently a new homologous series of compounds Srn−1Cun+1O2n have been reported in which the planes contain a parallel array of line defects which form a trellis lattice with ladder-segments of the square lattice weakly coupled through triangular line defects. The width of the ladder segments is determined by the parameter n and varies from single chains to arbitrarily wide ladders. The magnetic properties of undoped compounds will be dominated by the properties of the ladders. Heisenberg s = 1/2 ladders can have a spin liquid groundstate with a spin gap if the number of rungs is odd so that a short range RVB groundstate is predicted for such trellis lattices. Using a t-J model to describe the doped material leads to the prediction of a d-wave RVB superconducting groundstate with a large spin gap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754945
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  • 9
    Electronic Resource
    Electronic Resource
    On the phenomenology of superconductivity in cuprate materials (1994)
    Springer
    Journal of low temperature physics 95 (1994), S. 389-393 
    Details
    ISSN: 1573-7357
    Keywords: 74.20.De ; 74.70.Mq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Consequences of d-wave pairing on the macroscopic properties of a superconductor are analyzed. A decisive experiment to probe the symmetry of the pairing wave function is discussed. It is shown that the magnetic properties of granular high temperature superconductors can be understood on the basis of d-wave superconductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754955
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  • 10
    Electronic Resource
    Electronic Resource
    Theory of diffuse atom scattering from isolated adatoms (1985)
    Springer
    The European physical journal 59 (1985), S. 299-309 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The differential cross-section around specular for scattering off an isolated adatom on a metal surface with vanishing corrugation is calculated. The repulsive interaction part is modelled by a hard-wall potential; the attractive interaction is the sum of two soft potentials ascribed to the clean surface and the adatom, respectively. In a way similar to Watson's two-potential formula the scattering amplitude is expressed as the sum of a soft-potential contribution and a hard-core term. Assuming a high incident energy, these are calculated explicitly in a generalized form of the eikonal and the Kirchhoff approximation, respectively. Numerical calculations reveal a moderate, but significant enhancement of the scattering intensity around specular due to an interference of the adatom potential with the clean-surface interaction. The former causes a strong sharpening of the specular peak (compared to hard-core scattering).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307435
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