1PO1-61 The Origin of 2e factor in Josephson Effects
J.D. Fan and Y.M. Malozovsky, Department of Physics, Southern University and A&M College, P.O. Box 9767, Baton Rouge, LA 70813, USA
Presenting Author: J.D. Fan
It has been widely believed that the 2e factor in Josephson effects and quantization of the magnetic flux in a bored superconducting cylinder is the explicit evidence of Cooper's pairs of electrons. However, to the best knowledge of the authors, this belief is just a claim without any strict examination and proof. Following the previous work [1], the authors have shown, based on Berry's phase, that the 2e factor originates from the gauge invariance and London equation. Therefore, the 2e factor in Josephson effects has nothing to do with Cooper's pairing. This implies that the concept of Cooper's pairing is purely hypothetical and the understanding of the mechanism of superconductivity based on this concept may be skeptical. This result seems to provide a room for one to reconsider the mechanism of superconductivity in order to unify the theory for both low- and high-temperature superconductivity.
[1] Y.M. Malozovsky and J.D. Fan, Physics Letters A, 257 (1999) 332-337.
1PO1-62 Non-Adiabatic Aspects of Superconducting State Formation
Pavol Banacky 1,2, Michal Svrcek 2, and Anton Zajac 1,2. 1 Institute of Chemistry, Chemical Physics division, Faculty of Natural Science, Comenius University, Mlynska dolina CH2, 84212 Bratislava. 2 S-Tech a.s., Urulinska 3, 81101 Bratislava, Slovakia.
Presenting Author: P. Banacky
Unitary, P, Q-dependent, transformation of the general form of a molecular/solid state hamiltonian, i.e. hamiltonian of an assembly of interacting atoms was performed, resulting in seemingly complicated, but physically convenient transformed form of a quasiparticle hamiltonian. After introduction of the Fermi sea over the Wick`s theorem, the simultaneous optimization of the electronic and nuclear motion with respect to the coordinates and momenta of nuclei was performed. Obtained solution of the optimization is on non-adiabatic level, i.e. beyond the Born-Oppenheimer adiabatic approximation, yielding the ground-state energy correction, one-particle (electronic) spectrum correction, two-particle, i.e. correlation energy correction as well as, self-consistently corrected vibration (phonon) spectrum.
In view of these results, new insight on superconducting state formation is presented. Both the conditions of the transiton from normal to superconducting state, and basic equations characteristic for superconducting state (gap, electronic specific heat,...) have been specified and derived. Theoretical calculations of the temperature dependence of the photoemission (and tunneling) spectra of high-temperature superconductors have also been performed. The obtained results simulate correctly the experimental spectra, including very peculiar character of the temperature-dependent spectral changes near the Fermi surface.
The non-adiabatic theory offers an integrated platform for concurent study of both, conventional low-temperature superconductors and new high-temperature superconductors from the same theoretical stand-point without introduction of any auxiliary and/or exotic mechanisms.
1PO1-64 An Analysis of the Insulating and Normal Phases of High-Tc Systems
Ranjan Chaudhury, S.N. Bose National Centre For Basic Sciences, Block-JD, Sector-3, Salt Lake, Calcutta 700091, India
Presenting Author: R. Chaudhury
The excitations for two-dimensional quantum anisotropic antiferromagnetic Heisenberg model, as appropriate to the insulating phase of the oxide superconductors, are analysed. The possible consequences of the presence of topological excitations in the small and intermediate length scales are discussed. The various proposed microscopic origins of the anomalies observed in the normal state properties of the oxide superconductors are also explored. In particular, the conjecture that the normal phase contains bound fermion pairs, is critically examined.
1PO1-65 A Quantum Force in Superconductors
Alexey V. Nikulov, Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia
Presenting Author: A.V. Nikulov
It is well known that the superconducting state differs from a state with infinite conductivity because the superconductivity is a macroscopic quantum phenomena. A magnetic flux can change at the transition to the superconducting state, as it takes place at the Meissner effect and other phenomena connected with the quantization of the superconducting electron velocity. This change is induced by the superconducting current which appears because state with zero velocity of superconducting electrons is forbidden in some case. The electrons accelerate against the force of electric field which appears in accordance with the Faraday's law. This means that a quantum force can act at the transition to the superconducting state. In the consequence of this force a voltage with direct component can appear in a superconducting section of a ring if other section is switched iteratively from the superconducting to norman state and backwards [1]. Such ring can be considered as direct-current generator. A mechanical energy can be transformed in electric energy in a mesoscopic superconducting ring closed by a Josephson junction. Nature and significance of the quantum force are considered in the present work.
[1] A.V. Nikulov and I.N. Zhylyaev, J. Low Temp. Phys.112. 227 (1998).
1PO1-66 Calculation of Hole Distribution in YBa2Cu3O7-d
L.L. Cheng, X.T. Tang, and H. Zhang, Materials Physics Laboratory, State Key Laboratory for Artificial Microstructure and Mesoscope Physics, Department of Physics, Peking University, Beijing 100871, China
Presenting Author: H. Zhang
Separating the unit cell of YBa2Cu3O7-d into perovskite and rock salt blocks and considering the interaction between the two blocks, a computer program has been developed to calculate the interaction between the blocks, called combinative energy. The combinative energy in the YBa2Cu3O7-d with the different d value, from 0.07 to 0.62, was calculated. A close relationship between the superconducting transition temperature and the combinative energy in the YBa2Cu3O7-d is established, and the change of the combinative energy is closely related with the transformation from orthorhombic I to II. In order to compensate for the deficiency of the ionic model for the YBa2Cu3O7-d , we directly put some holes on the different planes in the YBa2Cu3O7-d . When the holes on the Cu(2)-O plane, the calculated result is perfectly consistent with the experimental one. When the holes on the 4 corners of the Cu(1)-O plane, there also exists a close relationship between the combinative energy and the oxygen deficiency, like the holes on the Cu(2)-O plane. But, when the holes are on the center of the Cu(1)-O plane, there is no such relationship. When the holes are on the Ba-O plane, the relationship between the combinative energy and the oxygen deficiency is ambiguous. The calculation of the holes on different planes supplies abundant information about the charge distribution in the YBa2Cu3O7-d . Comparing the calculating results and the experimental facts, it is believed that the interaction between the two blocks in the unit cell is of great importance to the superconductivity in the YBa2Cu3O7-d .
1PO1-67 Effective Sublattice Magnetization and Neel Temperature in Quantum Antiferromagnets
Eduardo C. Marino and Marcello B. Silva
Neto, Institudo de Física, Universidade Federal do Rio de
Janeiro, Caixa Postal 68528, Rio de Janeiro - RJ, 21945-970, Brazil
Presenting Author: Marcello B. Silva Neto We present an analytic expression for the finite temperature
sublattice magnetization in quantum antiferromagnets, for the whole range
of temperatures between 0 and TN. Our expression, which has no
adjustable parameters, is able to reproduce both the qualitative behavior
of the
phase diagram M(T) x T and the experimental values of the Néel
temperature,
for either doped
YBa2Cu3O6.15 and stoichiometric
La2CuO4 compounds.
The key mechanism for obtaining such an expression is the use of
the effective field theory approach to the continuum description of the
2D Heisenberg antiferromagnets at finite temperatures. We construct
an effective field theory, from the finite temperature nonlinear sigma
model with short range Néel order, by coarsing over the short
wavelength
degrees of freedom of the spin-wave fields about a state with short range Néel
order. The resulting effective field theory is shown to be characteri
zed by a
net effective sublattice magnetization which can be used as order parameter
for the destruction of antiferromagnetic order at finite temperatures.
We have found a remarkable agreement between our theoretical
predictions and experiment, already at the leading order of the large N
expansion,
for the whole range of temperatures up to the Néel critical point.
1PO1-68
Percolation of Superconductivity Grzegorz Litak, Department
of Mechanics, Technical University of Lublin, Nadbystrzycka 36,
PL-20-618 Lublin, Poland, and Balazs L. Gyorffy, H.H. Wills
Physics Laboratory, University of Bristol, Tyndall Ave, Bristol
BS8 1TL, United Kingdom Presenting Author: G. Litak In case of superconductors
whose electrons attract each other only if they are near certain
centers, the question arises 'How many of such centers are needed
to make the ground state superconducting?' We shall examine it in
the context of a random U Hubbard model. In short we study the
case where Ui is –½ U½ and 0 with probability c and 1-c
respectively on a lattice whose sites are labelled I using the
Gorkov decoupling and Coherent potential Approximation (CPA). We
argue that for this model there is a critical concentration c0
below which the system is not a superconductor. 1PO1-69
Quantum Tunneling Cyclic Loop in High Temperature Superconductor
Probably Is the Microscopic Origin of High Temperature
Superconductivity Dawei Zhou, R & D Dept.,
General Superconductor, Inc., P.O. Box 13981, Gainesville, FL
32604, USA Presenting Author: D. Zhou 4-particle (electrons or
electrons with hole) or higher order quantum tunneling cyclic
loops (QTCLs) in real space may play a key role in high Tc
superconductivity. Because of the existence of mixed valences on
the CuO2 plane, the electron/holes in high Tc
superconductor are weekly localized and strongly correlated thus
able to form CTCL. The QTCLs have k=0 in the center of the mass
frame, and a non-zero angular momentum. Each QTCL has total spin
S=0. Each QTCL can contain 2 or more Cooper pairs in real space.
As a result of the strong correlation between those tunneling
loops, high Tc superconductivity will occur if the
connectivity of tunneling loops is large enough to form an
infinite cluster, under these conditions: T<Tc and
H<Hc. This high Tc superconducting transition is
strong angular momentum related, is a special kind of percolation
transition which is consistent with the experimental results of
uniaxial stress experiments and of thermal expansion
measurements. This model is consistent with the fact that the
coherence length of high temperature superconductor is in the
order of 5-20 angstroms. QTCL model is consistent with gauge
invariance and the observation of doped carbon 60 superconductors
and superfluid 3He.