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  • Electronic Resource  (8)
  • 1985-1989  (6)
  • 1965-1969  (2)
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  • Electronic Resource  (8)
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  • 1
    Electronic Resource
    Electronic Resource
    Temperature and purity dependence of the nuclear-spin relaxation rate in the gapless region of type-II superconductors (1966)
    Springer
    The European physical journal 197 (1966), S. 46-57 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The volume average of the nuclear-spin relaxation rate in type-II superconductors,R s, is calculated for magnetic fields slightly below the upper critical field and all mean free paths,l, and temperatures. It is found to be expressible solely in terms of the volume average of the density of states, $$\bar N(\omega )$$ , where the latter quantity has been determined recently byNeumann for alll. The derivation is based onHelfand andWerthamer's eigen-value equation for the order parameter,Δ. The deviation of $$\bar R_s $$ from the relaxation rate in the normal state,R n, is proportional to the quantity $$[|\overline {\Delta |^2 } /\Delta _{BCS}^2 (T)]R_n $$ (the bar denotes the spatial average). The proportionality factor is found to decrease monotonously as the temperature decreases and/orl increases. This behavior is closely related to the fact that $$\bar N(\omega )$$ shows no gap for the excitation energiesω and decreases asl increases, in particular at energiesω close to zero (ω=0 corresponds to the Fermi energy).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01333085
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Theory of the density of states of pure type-II superconductors in high magnetic fields (1967)
    Springer
    The European physical journal 201 (1967), S. 209-221 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper deals with the theory of the density of states of pure type-II superconductors in high magnetic fields. An approximate expression of theGreen's function is derived by using the fact that it has the periodicity of the lattice of flux lines in the center-of-mass coordinates. In comparison to the normal stateGreen's function a correction term proportional to the absolute square of the order parameter arises. This is seen to act as a self-energy part depending strongly on the polar angleΘ of the “quasiparticle” momentum relative to the direction of the field. The corresponding density of states, as a function of the excitation energy, is found to vary from the gapless to the BCS type as the parameterΘ changes fromπ/2 to zero (orπ). The averaged state density varies gradually from a uniform to a BCS-like state density as the external field decreases sufficiently far below the upper critical field. The results of the present theory for the averaged density of states agree fairly well with the results due to a conjecture byMaki if the field is very close to the upper critical field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01326812
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Theory of the generalized Ginzburg-Landau parameter κ2 for strong-coupling superconductors at arbitrary impurity concentration (1989)
    Springer
    Journal of low temperature physics 77 (1989), S. 235-256 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study strong-coupling effects on the slope of the magnetization curve at the upper critical field of a type II superconductor, parametrized by the generalized Ginzburg-Landau parameter κ2. The use of the quasiclassical approach to the BCS-Gorkov theory, valid for all temperatures, allows us to present the calculations in a transparent manner. We obtain closed expressions for κ2 in terms of the solution of the eigenvalue problem determining the upper critical field, which we evaluate numerically. In the weak-coupling limit, previous results are reproduced, apart from a small correction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681534
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  • 4
    Electronic Resource
    Electronic Resource
    A simple interpolation method for the free energy of a type II superconductor in the mixed state (1987)
    Springer
    Journal of low temperature physics 66 (1987), S. 55-67 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A simple interpolation method is proposed for the construction of a surprisingly accurate free energy of a type II superconductor, which uses only properties at the upper and lower critical fields. The validity of the approach is checked against exact numerical results. The interpolation formula yields very good magnetization curves. For low-κ, type II superconductors small systematic deviations are obtained, which tend to reduce the type II/1 region (vortex attraction). A proper discussion of these delicate effects requires a very precise knowledge of the free energy for all inductions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681467
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Transfer matrix analysis of the two-dimensional ANNNI model (1985)
    Springer
    The European physical journal 59 (1985), S. 317-323 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The two-dimensional axial next-nearest neighbour Ising (ANNNI) model is studied for the first time by a transfer matrix method for semi-infinite strips (N×∞;N≦13). One obtains the thermodynamic properties and, more important, the correlation functions, which display directly the various magnetic structures. In one part of the phase diagram where a disorder line is believed to follow closely the ferromagnetic transition line the critical exponents appear to deviate from the expected ones. ForN≧13 a variational procedure is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307437
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  • 6
    Electronic Resource
    Electronic Resource
    Nonlinear analysis of spatial structures in two-dimensional anisotropic pattern forming systems (1986)
    Springer
    The European physical journal 63 (1986), S. 121-130 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Motivated in particular by recent experiments on convective instabilities in nematic liquid crystals we examine the possible stationary patterns in anisotropic quasi-two-dimensional systems. The generalized SH-model we use exhibits the typical Lifshitz point, which separates the regions of normal and of oblique rolls at threshold. Above threshold the two-dimensional wavenumber regions of stable roll solutions take on interesting shapes in the vicinity of the Lifshitz point. Undulated (wavy) rolls also exist metastably in a narrow parameter range. We derive envelope equations which show that this scenario is general near threshold. Our results suggest experimental investigation, especially in the neighborhood of the Lifshitz point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01312586
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Thermodynamic behaviour of type II superconductors at low induction for arbitrary temperature and impurity content (1987)
    Springer
    The European physical journal 68 (1987), S. 49-56 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using Eilenberger's equations in vortex symmetry, we calculate numerically the structure of an isolated flux line and the lower critical field of a type II superconductor as functions of temperature and impurity content. In order to describe in addition the low-induction regime of the mixed state, a circular-cell approximation is introduced and compared with recent exact results of the Eilenberger theory. The agreement is excellent, if the flux-line overlap is weak. Within this approach it is shown that the nature of the phase transition at the lower critical field depends very sensitively on anisotropies of the Fermi surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307863
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  • 8
    Electronic Resource
    Electronic Resource
    Depinning and wetting in two-dimensional Potts and chiral clock models (1987)
    Springer
    The European physical journal 69 (1987), S. 295-301 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The interplay of depinning and interfacial adsorption or wetting phenomena is studied for two-dimensional three-state Potts and chiral clock models where the variables on opposite boundaries are fixed in different states and the interactions near one of the surfaces are weakened compared to the ones in the bulk. Using a transfer matrix approach and Monte Carlo techniques a new interfacial multicritical point is found at which both interfacial properties become critical simultaneously. However, in general the two types of transitions are decoupled.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307288
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    Paper (German National Licenses)
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