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1.
P. Brovetto V. Maxia M. Salis 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(1):85-94
This paper presents a study whose aim is to decide whether the basic mechanism of electron pairing is the same for all unconventional
superconductors such as perovskites, cuprates, organic compounds and alkaly-stuffed fullerene. By analyzing the features of
these dissimilar materials, arguments are singled out showing that superconduction is originated by electrons combined in
weakly bound pairs running in regions bordering on certain lattice discontinuities which are common to the structure of the
superconductors dealt with. Special attention is devoted to the properties of the YBCO cuprate.
Received 3 November 1999 and Received in final form 18 May 2000 相似文献
2.
K. Krug K. Winzer M. Reiffers J. Kunes P. Novák F. Kayzel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):595-600
The Fermi surface of PrNi5 has been studied by the measurements of the de Haas-van Alphen (dHvA) effect at temperatures between 0.3 and in magnetic fields up to 12 T. Two dHvA frequencies have been obtained. The electronic structure of PrNi5 was calculated using the full potential linearized augmented plane wave method. Five sheets of the Fermi surface and the
multiple extremal cross sections were determined. First and second sheet have a hole-like structure. The agreement between
theory and experiment is obtained by a small downward shift ( 0.1 eV) of the Fermi energy which is probably due to an underestimation of the role of 4
f electrons.
Received 9 May 2000 and Received in final form 20 September 2000 相似文献
3.
D. Beckmann S. Wanka J. Wosnitza J.A. Schlueter J.M. Williams P.G. Nixon R.W. Winter G.L. Gard J. Ren M.-H. Whangbo 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):295-300
The electronic structure of the quasi two-dimensional (2D) organic superconductor -(ET)2SF5CH2CF2SO3 was examined by measuring Shubnikov-de Haas (SdH) and angle-dependent magnetoresistance (AMRO) oscillations and by comparing
with electronic band-structure calculations. The SdH oscillation frequencies follow the angular dependence expected for a 2D Fermi surface (FS), and the observed fundamental frequency shows that the 2D FS is 5%
of the first Brillouin zone in size. The AMRO data indicate that the shape of the 2D FS is significantly non-circular. The
calculated electronic structure has a 2D FS in general agreement with experiment. From the temperature and angular dependence
of the SdH amplitude, the cyclotron and band effective masses were estimated to be and ,where g is the conduction electron g factor and the free electron mass. The band effective mass is estimated to be from the calculated electronic band structure.
Received: 3 March 1997 / Revised: 5 May 1997 / Received in final form: 5 November 1997 / Accepted: 10 November 1997 相似文献
4.
D. Beckmann S. Wanka J. Wosnitza G. Goll B. Drehmann E. Balthes D. Schweitzer W. Strunz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):329-333
We report on Shubnikov-de Haas and de Haas-van Alphen measurements of an organic metal based on the molecular donor bis(ethylenedioxy)-tetrathiavulvalene
(= BEDO-TTF) and the anion Cl- with H2O molecules. The observed single oscillation frequency perfectly follows the two-dimensional dependence with T. The Fermi-surface area of of the first Brillouin zone proves a quarter-filled band, i.e., a 2:1 stoichiometry of the BEDO-TTF donor with respect to the anion. The apparent discrepancy to X-ray data which give a
1:1 ratio between BEDO-TTF and Cl- is understood by replacement of H2O molecules with (H3O)+ ions. The proposed stoichiometry therefore is (BEDO-TTF)2
+(H5O2)+(Cl-)2. The cyclotron effective mass is when deduced from the temperature dependence of the fundamental oscillation amplitude, but strongly reduced when extracted
from higher harmonics. This and the strong harmonic content of the oscillations signals an influence of the two-dimensional
electronic structure and can be qualitatively understood by applying the concept of magnetic interaction to the effect of
the oscillatory chemical potential.
Received: 16 April 1998 / Revised: 7 July 1998 / Accepted: 9 July 1998 相似文献
5.
P. Tarasewicz 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(1):33-45
The thermodynamics of an extended BCS
model of superconductivity is investigated. A physical system is
described by a Hamiltonian containing the BCS interaction and an
attractive four-fermion interaction. The four-fermion potential is
caused by attractions between Cooper pairs mediated by the phonon
field. The weakness of this potential allows the use of
perturbation theory. The perturbation expansion was restricted to
the first order because in the ground state the second order terms
are not larger than 0.5 percent of first order correction for
parameters used for calculations. The BCS Hamiltonian is an
unperturbed one. The ground state and the thermal properties are
examined. As a result the jump in the specific heat is higher than
that in the BCS case. Moreover, the squared critical field is
larger than the corresponding one in the BCS theory. Additionally,
we show connections with the Bogolyubov's mean field approach used
earlier in order to investigate general physical consequences of
the model. 相似文献
6.
P. Schwaller T. Greber P. Aebi J.M. Singer H. Berger L. Forró J. Osterwalder 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):215-225
Full k
-maps of the electronic structure near the Fermi level of differently doped cuprates measured with angle-scanned photoelectron
spectroscopy are presented. The valence band maximum of the antiferromagnetic insulator Sr2CuO2Cl2, which is taken as a representative of an undoped cuprate, and the Fermi surfaces of overdoped, optimally doped and underdoped
Bi2Sr2CaCu2O8+δ high-temperature superconductors are mapped in the normal state. The results confirm the existence of large Luttinger Fermi
surfaces at high doping with a Fermi surface volume proportional to (1+x), where x is the hole concentration. At very low doping, however, we find that this assumption based on Luttinger's theorem is not
fulfilled. This implies a change in the topology of the Fermi surface. Furthermore the intensity of the shadow bands observed on the Fermi surface of Bi2Sr2CaCu2O8+δ as a function of the doping is discussed.
Received 12 October 1999 and Received in final form 12 April 2000 相似文献
7.
A. Liebsch H. Ishida 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):405-411
There exists presently considerable debate over the question whether
local Coulomb interactions can explain the absence of the small e′
g
Fermi surface hole pockets in photoemission studies of Na0.3CoO2.
By comparing dynamical mean field results for different single particle
Hamiltonians and exact diagonalization as well as quantum Monte Carlo
treatments, we show that, for realistic values of the Coulomb energy U
and Hund exchange J, the e′
g pockets can be slightly enhanced or
reduced compared to band structure predictions, but they do not disappear. 相似文献
8.
P. Brovetto V. Maxia M. Salis 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):331-334
The superconducting properties of materials of layered structure containing copper and other metal oxides are compared with
the expectations ofa recently proposed electron pairing model 1. The role of the oxygen content of samples is emphasized. Evidence is found showing that superconduction is originated only
in presence of coupled layers of metal oxides holding unpaired electrons.
Received 8 November 2000 相似文献
9.
D. Vignolles V. N. Laukhin A. Audouard M. Nardone T. G. Prokhorova E. B. Yagubskii E. Canadell 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):53-60
The Shubnikov-de Haas (SdH) oscillation spectra of the
-(BEDT-TTF)4(NH4)[ Cr(C2O4)3] .DMF
organic metal have been studied in pulsed magnetic fields of up to
either 36 T at ambient pressure or 50 T under hydrostatic
pressures of up to 1 GPa. The ambient pressure SdH oscillation
spectra can be accounted for by up to six fundamental frequencies
which points to a rather complex Fermi surface (FS). A noticeable
pressure-induced modification of the FS topology is evidenced
since the number of frequencies observed in the spectra
progressively decreases as the pressure increases. Above 0.8 GPa,
only three compensated orbits are observed, as it is the case for
several other isostructural salts of the same family at ambient
pressure. Contrary to other organic metals, of which the FS can be
regarded as a network of orbits, no frequency combinations are
observed for the studied salt, likely due to high magnetic
breakdown gap values or (and) high disorder level evidenced by
Dingle temperatures as large as ≃7 K. 相似文献
10.
R. Kishore S. Lamba 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):161-164
An exact analytical expression for the specific heat jump at the critical temperature Tc has been obtained directly from the BCS gap equation for any shape of the energy dependent electronic density of states (DOS).
We consider a model which takes into consideration electron-electron repulsion, formulated in the Hubbard model along with
the electron-electron attraction due to electron-phonon interaction in the BCS formalism. We have analyzed this expression
for constant as well as for the Lorentzian forms of DOS. It is shown that the constant DOS in the simple BCS theory cannot
explain the large values of , found in some superconductors. The specific heat versus temperature curve has been found to have a peak, similar to that of Eliashberg theory of superconductivity. The influence
of repulsive interaction is very small and occurs mainly at higher temperatures.
Received: 26 January 1998 相似文献
11.
C. Battaglia H. Cercellier L. Despont C. Monney M. Prester H. Berger L. Forró M. G. Garnier P. Aebi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(4):385-390
Magnetic ordering of the first row transition metal
intercalates of NbS2 due to coupling between the conduction
electrons and the intercalated ions has been explained in terms of
Fermi surface nesting. We use angle-resolved photoelectron
spectroscopy to investigate the Fermi surface topology and the
valence band structure of the quasi-two-dimensional layer compounds
Mn1/3NbS2 and Ni1/3NbS2. Charge transfer from the
intercalant species to the host layer leads to non-uniform, pocket
selective doping of the Fermi surface. The implication of our
results on the nesting properties are discussed. 相似文献
12.
J. Kokalj P. Prelovšek 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):431-435
The frequency-moment expansion method is developed to analyze the validity of the Luttinger sum rule within the Mott-Hubbard
insulator, as represented by the generalized Hubbard model at half filling and large U. For the particular case of the Hubbard model with nearest-neighbor hopping on a triangular lattice lacking the particle-hole
symmetry results reveal substantial violation of the sum rule. 相似文献
13.
M. M. Korshunov S. G. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):271-278
In this paper a mean-field theory for the spin-liquid paramagnetic non-superconducting phase of the p- and n-type high-Tc cuprates is developed. This theory applied to the effective t-t'-t′′-J* model with the ab initio calculated parameters and with the three-site correlated hoppings. The static spin-spin and kinematic
correlation functions beyond Hubbard-I approximation are calculated self-consistently. The evolution of the Fermi surface
and band dispersion is obtained for the wide range of doping concentrations x. For p-type systems the three different types
of behavior are found and the transitions between these types are accompanied by the changes in the Fermi surface topology.
Thus a quantum phase transitions take place at x = 0.15 and at x = 0.23.Due to the different Fermi surface topology we found
for n-type cuprates only one quantum critical concentration, x = 0.2. The calculated doping dependence of the nodal Fermi
velocity and the effective mass are in good agreement with the experimental data. 相似文献
14.
E. Forzani K. Winzer 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):29-40
High quality samples and absence of superconductivity down to 40 mK
make of ZrB2 the best normal state reference system for the superconducting
isostructural MgB2. Actually, the question of pairing has to be focused on
the electron-phonon interaction in the normal state. After presenting the
resistivity measurements of ZrB2, we explain the details of the
Bloch-Grüneisen and Einstein models used to deduce the first results. We then
compare experimental de Haas-van Alphen effect data with theoretical Fermi
surfaces to present additional results on electron quasi-particle
renormalization. The estimations reveal an isotropic and negligible coupling
constant of in average
0.145. The
contribution of the coupling to the optical phonon modes is 0.082, in contrast
to the known larger coupling of 0.283 [3] to the E2g phonon mode
in MgB2. 相似文献
15.
C. Proust A. Audouard V. Laukhin L. Brossard M. Honold M.-S. Nam E. Haanappel J. Singleton N. Kushch 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):31-37
We report on the inter-layer oscillatory conductance of the two-dimensional organic superconductor (BEDO-TTF)2ReO4H2O measured in static and pulsed magnetic fields of up to 15 and 52 T, respectively. In agreement with previous in-plane studies,
two Shubnikov-de Haas oscillation series linked to the two electron and the hole orbits are observed. The influence of the
magnitude and orientation of the magnetic field with respect to the conducting plane is studied in the framework of the conventional
two- and three-dimensional Lifshits-Kosevich (LK) model. Deviations of the data from this model are observed in low fields
strongly tilted with respect to the normal to the conducting plane. In this latter case, the observed behaviour is consistent
with an unexplained lowering of the cyclotron effective mass. At high magnetic field, the oscillatory data could have been
compatible with the occurrence of a magnetic breakdown orbit built from the hole and electron orbits. However, the increase
of the cyclotron effective mass, linked to the electron orbits, as the magnetic field increases above ∼12 T is consistent with a field-induced phase transition. In the lower field range, where the conventional LK model holds,
the analysis of the angle dependence of the oscillations amplitude suggests significant renormalisation of the effective Landé
factor.
Received 22 August 2000 and Received in final form 20 December 2000 相似文献
16.
O.V. Danylenko O.V. Dolgov M.L. Kulic V. Oudovenko 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):201-206
By assuming that the superconducting pairing is due to the forward E-P scattering (FEP pairing) it is shown that the critical temperature of clean systems depends linearly on the E-P coupling constant and the isotope effect is very small. Impurities with the pronounced forward scattering (FS impurities) change analytical properties of the quasiparticle Green's function substantially compared to the case of the
isotropic scattering. The FS impurities are pair-breaking and affect in the same way s- and d-wave
FEP pairing making in the dirty limit.The usual isotropic impurity scattering is pair-weakening for s-wave and pair-breaking for the d-wave
FEP pairing.
Received 1st July 1998 相似文献
17.
C. Dziurzik A. Schadschneider J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):209-216
We investigate the stability domains of ground states of generalized Hubbard models with next-nearest neighbour interaction
using the optimum groundstate approach. We focus on the -pairing state with momentum P=0 and the fully polarized ferromagnetic state at half-filling. For these states exact lower bounds for the regions of stability
are obtained in the form of inequalities between the interaction parameters. For the model with only nearest neighbour interaction
we show that the bounds for the stability regions can be improved by considering larger clusters. Additional next-nearest
neighbour interactions can lead to larger or smaller stability regions depending on the parameter values.
Received 30 March 1999 and Received in final form 3 May 1999 相似文献
18.
E.A. Smirnova P.A. Korzhavyi Yu. Kh. Vekilov B. Johansson I.A. Abrikosov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):57-66
We report on a detailed investigation of the phase equilibria and the Fermi surface in the Al-Zn system. Our calculation are
based on the density functional theory and we use the linear muffin-tin orbital method and the Green's function technique.
The calculated free energies of alloy formation exhibit the existence of a miscibility gap between the alloys containing approximately
10 and 55 at.% of Zn, in agreement with the phase diagram of the Al-Zn system. Seven electronic topological transitions (ETT)
were found in Al-Zn system within the stability range of the fcc solid solution. A relation between these ETT and the phase
stability of the fcc Al-Zn solid solutions is established. We show that extremum points on the concentration dependencies
of the thermodynamic properties of Al-Zn alloys can be explained by band-filling effects.
Received 6 February 2002 Published online 19 November 2002 相似文献
19.
S. Chakravarty 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):337-343
The interlayer tunneling mechanism of the cuprate high temperature superconductors involves a conversion of the confinement
kinetic energy of the electrons perpendicular to the CuO-planes (c-axis) in the normal state to the pair binding energy in the superconducting state. This mechanism is discussed and the arguments
are presented from the point of view of general principles. It is shown that recent measurements of the c-axis properties support the idea that the electrons substantially lower their c-axis kinetic energy upon entering the superconducting state, a change that is nearly impossible in any conventional mechanism.
The proper use of a c-axis conductivity sum rule is shown to resolve puzzles involving the penetration depth and the optical measurements.
Received: 5 January 1998 / Accepted: 17 March 1998 相似文献
20.
D. Vignolles A. Audouard L. Brossard S. Pesotskii R. Lyubovskii M. Nardone E. Haanappel R. Lyubovskaya 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):53-61
Interlayer magnetoresistance and magnetisation of the quasi-two dimensional organic metal (BEDT-TTF)8Hg4Cl12(C6H5Br)2 have been investigated in pulsed magnetic fields extending up to 60 T and 33 T, respectively. About fifteen fundamental frequencies,
composed of linear combinations of only three basic frequencies, are observed in the oscillatory spectra of the magnetoresistance.
The dependencies of the oscillation amplitude on the temperature and on the magnitude and orientation of the magnetic field
are analyzed in the framework of the conventional two-dimensional Lifshitz-Kosevitch (LK) model. This model is implemented
by damping factors which accounts for the magnetic breakthrough occurring between electron and hole orbits yielding conventional
Shubnikov-de Haas closed orbits (model of Falicov and Stachowiak) and quantum interferometers. In particular, a quantum interferometer
enclosing an area equal to the first Brillouin zone area is evidenced. The LK model consistently accounts for the temperature
and magnetic field dependence of the oscillation amplitude of this interferometer. On the contrary, although this model formally
accounts for almost all of the observed oscillatory components, it fails to give consistent quantitative data in most other
cases.
Received 4 September 2002 / Received in final form 14 November 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: audouard@insa-tlse.fr
RID="b"
ID="b"UMR 5830: Unité Mixte de Recherche CNRS - Université Paul Sabatier - INSA de Toulouse
RID="c"
ID="c"UMS 5642: Unité Mixte de Service CNRS - Université Paul Sabatier - INSA de Toulouse 相似文献