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1.
H. Capellmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):25-30
Superconductors put into rotation develope a spontaneous internal magnetic field (the “London field”). In this paper Ginzburg
Landau equations for order parameter, field, and current distributions for superconductors in rotation are derived. Two simple
examples are discussed: the massive cylinder and the “Little and Parks geometry”: a thin film of superconducting material
deposited on a cylinder of normal material. A dependence of T
c on rotational frequency is predicted. The magnitude of the effect is estimated and should be observable.
Received 28 May 2001 相似文献
2.
R.A. Ritchie H.G. Miller F.C. Khanna 《The European Physical Journal A - Hadrons and Nuclei》2001,10(1):97-100
Based on recent studies of the temperature dependence of the energy and specific heat of liquid nuclear matter, a phase transition
is suggested at a temperature ∼ 0.85 MeV. We apply the Landau-Ginzburg theory to this transition and determine the behaviour
of the energy and specific heat close to the critical temperature in the condensed phase.
Received: 29 July 2000 / Accepted: 20 October 2000 相似文献
3.
J.J. Betouras V.A. Ivanov F.M. Peeters 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):349-354
We present a model of pressure effects of a two-band superconductor based on a Ginzburg-Landau free energy with two order
parameters. The parameters of the theory are pressure as well as temperature dependent. New pressure effects emerge as a result
of the competition between the two bands. The theory then is applied to MgB2. We identify two possible scenaria regarding the fate of the two σ subbands under pressure, depending on whether or not both subbands are above the Fermi energy at ambient pressure. The splitting
of the two subbands is probably caused by the E2g distortion. If only one subband is above the Fermi energy at ambient pressure (scenario I), application of pressure diminishes
the splitting and it is possible that the lower subband participates in the superconductivity. The corresponding crossover
pressure and Gr neisen parameter are estimated. In the second scenario both bands start above the Fermi energy and they move below it, either
by pressure or via the substitution of Mg by Al. In both scenaria, the possibility of electronical topological transition is emphasized. Experimental
signatures of both scenaria are presented and existing experiments are discussed in the light of the different physical pictures.
Received 3 September 2002 / Received in final form 16 December 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: joseph.betouras@ua.ac.be
RID="b"
ID="b"On leave from N.S. Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, 31 Leninskii
prospekt, 117915, Moscow, Russia 相似文献
4.
G.G.N. Angilella G. Balestrino P. Cermelli P. Podio-Guidugli A.A. Varlamov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):67-74
We propose a Ginzburg-Landau phenomenological model for the dependence of the critical temperature on microscopic strain in
tetragonal high-T
c
cuprates. Such a model is in agreement with the experimental results for LSCO under epitaxial strain, as well as with the
hydrostatic pressure dependence of T
c
in most cuprates. In particular, a nonmonotonic dependence of T
c
on hydrostatic pressure, as well as on in-plane or apical microstrain, is derived. From a microscopic point of view, such
results can be understood as due to the proximity to an electronic topological transition (ETT). In the case of LSCO, we argue
that such an ETT can be driven by a strain-induced modification of the band structure, at constant hole content, at variance
with a doping-induced ETT, as is usually assumed.
Received 1st October 2001 and Received in final form 5 December 2001 相似文献
5.
N.A. Taylanov G.R. Berdiyorov 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):343-348
The problem of the thermal and magnetic destruction of the critical state in composite superconductors is investigated. The
initial distributions of temperature and electromagnetic field are assumed to be essentially inhomogeneous. The limit of the
thermomagnetic instability in quasi-stationary approximation is determined. The obtained integral criterion, unlike the analogous
criterion for a homogeneous temperature profile, is shown to take into account the influence of any part of the superconductor
on the threshold for critical-state instability.
Received 11 October 2001 / Received in final form 30 November 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: taylanov@iaph.tkt.uz 相似文献
6.
G. Stenuit S. Michotte J. Govaerts L. Piraux 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):103-107
Theoretical and experimental magnetizations of lead nanowire arrays well below the superconducting transition temperature
Tc are described. The magnetic response of the array was investigated with a SQUID magnetometer. Hysteretic behaviour and phase
transitions have been observed in sweeping up and down the external magnetic field at different temperatures. The Meissner
and Abrikosov states were also experimentally observed in this apparently type-I superconductor. This fact brings to the fore
the non-trivial behaviour of the critical boundary κ
c ( = 1/ in bulk materials) between type-I and type-II phase transitions at mesoscopic scales. The time-independent Ginzburg-Landau
equations particularized to cylindrically symmetric configurations enable one to explain and reproduce the experimental magnetization
curves within 10% of error.
Received 16 January 2003 / Received in final form 27 March 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: stenuit@fynu.ucl.ac.be 相似文献
7.
G. Pica A. Andreone F. Palomba M. Salluzzo R. Vaglio G. Malandrino V. Ancarani I.L. Fragalà A. Cassinese G. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):405-411
We report on the synthesis, structural and electrical characterization of high quality Tl2Ba2Ca1Cu2O8 (Tl-2212) superconducting films. The samples have been grown ex-situ on mm2 LaAlO3 (100) substrates by a combined approach of metal-organic chemical vapor deposition (MOCVD) and thallium vapor diffusion.
The morphological and compositional nature of the c-axis oriented films has been investigated by SEM and X-ray analyses. Typical values of K and MA/cm2 at 77 K have been measured. Microwave measurements have been performed at f
= 87 GHz inserting the film in a copper cavity and at f
=1.5 GHz on patterned samples using a microstrip resonator technique. A penetration depth nm is evaluated by fitting the microwave data with phenomenological equations. The minimum value of the surface resistance
measured at 4.2 K is 60 and 6 m at 1.5 GHz and 87 GHz respectively. The microwave data are described in the context of a modified two fluid model. An evaluation
of the temperature dependence of the scattering rate has been performed through the simultaneous measurement of the surface
resistance and the penetration depth.
Received 16 December 1999 and Received in final form 17 March 2000 相似文献
8.
L. Benfatto A. Perali C. Castellani M. Grilli 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):609-612
We evaluate the charge and spin susceptibilities of the 2D attractive Hubbard model and we compare our results with Monte
Carlo simulations on the same model. We discuss the possibility to include topological Kosterlitz-Thouless superconducting
fluctuations in a standard perturbative approach substituting in the fluctuation propagator the Ginzburg-Landau correlation
length with the Kosterlitz-Thouless correlation length.
Received 30 June 1999 相似文献
9.
We discuss the excess conductivity at nonzero frequencies in a superconductor above Tc within the Gaussian approximation. We focus the attention on the temperature range not too close to Tc: within a time-dependent Ginzburg-Landau formulation, we phenomenologically introduce a short wavelength cutoff (of the order
of the inverse coherence length) in the fluctuational spectrum to suppress high momentum modes. We treat the general cases
of thin wires, anisotropic thin films and anisotropic bulk samples. We obtain in all cases explicit expressions for the finite
frequency fluctuational conductivity. The dc case directly follows. Close to Tc the cutoff has no effect, and the known results for Gaussian fluctuations are recovered. Above Tc, and already for ε = ln(T/T
c) > 10-2, we find strong suppression of the paraconductivity as compared to the Gaussian prediction, in particular in the real part
of the paraconductivity. At high ε the cutoff effects are dominant. We discuss our results in comparison with data on high-Tc superconductors.
Received 19 March 2002 Published online 25 June 2002 相似文献
10.
Transition to Fulde-Ferrel-Larkin-Ovchinnikov phases near the tricritical point: an analytical study
R. Combescot C. Mora 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):397-406
We explore analytically the nature of the transition to the Fulde-Ferrel-Larkin-Ovchinnikov superfluid phases in the vicinity
of the tricritical point, where these phases begin to appear. We make use of an expansion of the free energy up to an overall
sixth order, both in order parameter amplitude and in wavevector. We first explore the minimization of this free energy within
a subspace, made of arbitrary superpositions of plane waves with wavevectors of different orientations but same modulus. We
show that the standard second order FFLO phase transition is unstable and that a first order transition occurs at higher temperature.
Within this subspace we prove that it is favorable to have a real order parameter and that, among these states, those with
the smallest number of plane waves are preferred. This leads to an order parameter with a cos(
.
) dependence, in agreement with preceding work. Finally we show that the order parameter at the transition is only very slightly
modified by higher harmonics contributions when the constraint of working within the above subspace is released.
Received 20 February 2002 / Received in final form 4 June 2002 Published online 13 August 2002 相似文献
11.
12.
C. Ferdeghini V. Ferrando V. Braccini M.R. Cimberle D. Marré P. Manfrinetti A. Palenzona M. Putti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):147-151
The anisotropy of MgB2 is still under debate: its value, strongly dependent on the kind of sample and on the measuring method, ranges between 1.2
and 13. In this work we present our results on MgB2 c-oriented superconducting thin film. To evaluate the anisotropy, we followed two different approaches. Firstly, magnetoresistivity
was measured as a function of temperature at selected magnetic fields applied both parallel and perpendicular to the c-axis; secondly, we measured magnetoresistivity at selected temperatures and magnetic fields, varying the angle θ between the magnetic field and the c-axis. The anisotropy estimated from the ratio between the upper critical fields parallel and perpendicular to the c-axis and the one obtained in the framework of the scaling approach within the anisotropic Ginzburg-Landau theory are different
but show a similar trend in the temperature dependence. Some differences in the upper critical field and in its anisotropy
of our film with respect to single crystals are emphasized: some of these aspects can be accounted for by an analysis of upper
critical fields within a two-band model in presence of disorder and/or crystallographic strain.
Received 12 July 2002 / Received in final form 17 September 2002 Published online 29 November 2002 相似文献
13.
M. Camarda G.G.N. Angilella R. Pucci F. Siringo 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):273-277
The Gaussian Effective Potential in a fixed transverse unitarity gauge is studied for the static three-dimensional U(1) scalar
electrodynamics (Ginzburg-Landau phenomenological theory of superconductivity). In the broken-symmetry phase the mass of the
electromagnetic field (inverse penetration depth) and the mass of the scalar field (inverse correlation length) are both determined
by solution of the coupled variational equations. At variance with previous calculations, the choice of a fixed unitarity
gauge prevents from the occurrence of any unphysical degree of freedom. The theory provides a nice interpolation of the experimental
data when approaching the critical region, where the standard mean-field method is doomed to failure.
Received 18 November 2002 / Received in final form 26 March 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: giuseppe.angilella@ct.infn.it 相似文献
14.
We study the phase diagram of spatially inhomogeneous Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) superconducting state using the Ginzburg–Landau (GL) free energy, derived from the microscopic Hamiltonian of the system, and notice that it has a very clear Lifshitz tricritical point. We find the specific heat jumps abruptly near the first-order line in the emergent phase diagram which is very similar to the recent experimental observation in layered organic superconductor. Comparison with experimental data allows us to obtain quantitative relations between the parameters of phenomenological free energy. The region of the phase diagram where the specific heat jumps can be probed by doing a dynamical analysis of the free energy. 相似文献
15.
M. Takigawa M. Ichioka K. Machida 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):303-311
Thermal conductivity κ
xx(T) under a field is investigated in d
x2 - y2-wave superconductors and isotropic s-wave superconductors by the linear response theory, using a microscopic wave function of the vortex lattice states. To study
the origin of the different field dependence of κxx(T) between higher and lower temperature regions, we analyze the spatially-resolved thermal conductivity around a vortex at
each temperature, which is related to the spectrum of the local density of states. We also discuss the electric conductivity
in the same formulation for a comparison.
Received 8 December 2001 and Received in final form 20 March 2002 Published online 6 June 2002 相似文献
16.
Qiong-Gui Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):27-36
The interaction between a general magnetic source and a
long type-II superconducting cylinder in the Meissner or mixed state
is studied within the London theory. We first study the Meissner
state and solve the Maxwell–London equations when the source is a
magnetic monopole located at an arbitrary position. Then the field
and supercurrent for a more complicated magnetic charge distribution
can be obtained by superposition. A magnetic point dipole with
arbitrary direction is studied in detail. It turns out that the
levitation force on the dipole contains in general an angular as well
as a radial component. By integration we obtain the field and
supercurrent when the source is a two-dimensional monopole (a
magnetically charged long thread along the axial direction), from
which the results for a two-dimensional point dipole easily follow.
In the latter case the levitation force points in the radial
direction regardless of the orientation of the dipole. The case for a
current carrying long straight wire parallel to the cylindrical axis
is solved separately. The limit of ideal Meissner state is discussed
in most cases. The case of mixed state is discussed briefly. It turns
out that vortex lines along the axial direction and vortex rings
concentric with the cylinder have no effect outside the cylinder and
the levitation forces remain the same as in the case of the Meissner
state. 相似文献
17.
A. Agliolo Gallitto G. Bonsignore G. Giunchi M. Li Vigni 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):537-542
We discuss the microwave second-harmonic generation in
high-density bulk MgB2, prepared by the reactive liquid Mg
infiltration technology. The intensity of the harmonic signal has
been investigated as a function of temperature and amplitudes of
the DC and microwave magnetic fields. The results are discussed in
the framework of a phenomenological theory, based on the two-fluid
model, which assumes that both the microwave and static magnetic
fields, penetrating in the surface layers of the sample, weakly
perturb the partial concentrations of the normal and
superconducting fluids. We show that, in order to account for the
experimental results, it is essential to suppose that in MgB2
the densities of the normal and condensed fluids linearly depend
on the temperature. 相似文献
18.
Given the spectrum of a Hamiltonian, a methodology is developed which employs the Landau-Ginsburg theory for characterizing
phase transitions in infinite systems to identify phase transition remnants in finite fermion systems. As a first application
of our appproach we discuss pairing in finite nuclei. 相似文献
19.
A. Volmer M. Schwartz 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):211-218
In pure anisotropic or layered superconductors thermal fluctuations induce a van der Waals attraction between flux lines.
This attraction together with the entropic repulsion has interesting consequences for the low field phase diagram; in particular,
a first order transition from the Meissner phase to the mixed state is induced. We introduce a new variational approach that
allows for the calculation of the effective free energy of the flux line lattice on the scale of the mean flux line distance
a, which is based on an expansion of the free energy around the regular triangular Abrikosov lattice. Using this technique,
the low field phase diagram of these materials may be explored. The results of this technique are compared with a recent functional
RG treatment of the same system.
Received: 25 June 1996 / Revised: 18 August 1998 / Accepted: 21 August 1998 相似文献
20.
L. Benfatto S. Caprara C. Di Castro 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(1):95-102
We describe the spectral properties of underdoped cuprates as resulting from a momentum-dependent pseudogap in the normal-state
spectrum. Such a model accounts, within a BCS approach, for the doping dependence of the critical temperature and for the
two-parameter leading-edge shift observed in the cuprates. By introducing a phenomenological temperature dependence of the
pseudogap, which finds a natural interpretation within the stripe quantum-critical-point scenario for high- superconductors, we reproduce also the bifurcation near optimum doping. Finally, we briefly discuss the different role of the gap and the pseudogap in determining
the spectral and thermodynamical properties of the model at low temperatures.
Received 17 February 2000 相似文献