DC RESISTIVITY OF CHARGED COOPER PAIRS IN A SIMPLE BOSON-FERMION MODEL OF SUPERCONDUCTORS

2008 ◽  
Vol 22 (25n26) ◽  
pp. 4386-4397
Author(s):  
T. A. MAMEDOV ◽  
M. DE LLANO
Keyword(s):  
High Temperature Superconductors ◽  
Interaction Model ◽  
Energy Spectra ◽  
Gas Mixture ◽  
Cooper Pairs ◽  
Free Fermions ◽  
Interelectron Interaction ◽  
Self Consistent ◽  
Analytic Expression ◽  
Fermion Gas

An analytic expression for the contribution σB(λ, T) to the conductivity from charged bosonic Cooper pairs (CPs) is derived via two-time Green function techniques as a function of the BCS interelectron interaction model parameter λ and temperature T. Within the framework of a binary boson-fermion gas mixture model, it is shown that a self-consistent description of the resistivity data observed in high-temperature superconductors is possible only by assuming the presence of a finite gap between the energy spectra of free fermions and bosonic CPs.

UNIFORM COULOMB FIELD AS ORIGIN OF "FERMI ARCS" IN AN ANISOTROPIC BOSON-FERMION GAS MIXTURE

2013 ◽  
Vol 27 (29) ◽  
pp. 1347002 ◽  
Author(s):  
T. A. MAMEDOV ◽  
M. DE LLANO
Keyword(s):  
Coulomb Field ◽  
Absolute Temperature ◽  
Superconducting Gap ◽  
Gas Mixture ◽  
Cooper Pairs ◽  
Pair Breaking ◽  
Pseudogap Phase ◽  
Fermi Arcs ◽  
Binary Gas Mixture ◽  
Fermion Gas

A recent boson-fermion (BF) binary gas mixture model is extended to include: (i) anisotropy of the BF interaction and (ii) momentum-independent Coulomb repulsions. It is applied to account for the peculiarities of the pseudogap observed as function of absolute temperature T and concentration x of holes doped onto the CuO 2 planes and to study the further transformation of the pseudogap into the real superconducting gap, as T is lowered. Using two-time Green functions it is shown that pair breakings depend on the separation between the boson and fermion spectra of the BF mixture. As this separation shrinks, the pair-breaking ability of the Coulomb interaction weakens and disappears at the BEC Tc, i.e., at the T below which a complete softening of bosons occurs. Simultaneous inclusion of both effects (i) and (ii) produces, as T is lowered, "islands" in momentum space of incoherent Cooper pairs above the Fermi sea. These islands grow upon further cooling and merge together just before Tc is reached. The new extended BF model predicts a pseudogap phase in 2D high-Tc superconductors with lines of points, or loci, on the Fermi surface along which the pseudogap vanishes. This explains the origin of T-dependent "Fermi arcs" observed in ARPES experiments.

Thermodynamic characterization of high-temperature superconductors in the yttrium-barium-copper-oxygen system. The Y123 solid solution (Technical Report)

2000 ◽  
Vol 72 (3) ◽  
pp. 463-477 ◽  
Author(s):  
G. F. Voronin
Keyword(s):  
Solid Solution ◽  
Gibbs Energy ◽  
Thermodynamic Data ◽  
High Temperature Superconductors ◽  
Gibbs Energy Function ◽  
Data Set ◽  
Y123 Phase ◽  
Barium Copper ◽  
Self Consistent ◽  
Consistent Thermodynamic Data

The aim of this report is to inform the chemical community about a self-consistent thermodynamic data set for the YBa2 Cu3 O6+z (1 ≥ z ≥ 0) solid solution, that is well known as the Y123 phase and possesses superconducting properties at z~1 and low temperatures. About 3300 experimental points obtained in 240 miscellaneous experiments published in 78 papers have been processed simultaneously in order to obtain the most reliable Gibbs energy function of the Y123 phase in the temperature range from 250 to 1300 K and pressures up to 100 kbar. A function is recommended for approximation of the Gibbs energy, which has 16 adjustable parameters. All other thermodynamic properties of the Y123 solution, including the conditions for its internal stability, can be derived from the assessed Gibbs energy. Brief descriptions of the thermodynamic model, experimental and data assessment methods as well as examples of self-consistent thermodynamic data applications are given.

GENERALIZED BCS EQUATIONS: APPLICATIONS

2010 ◽  
Vol 24 (19) ◽  
pp. 3701-3712 ◽  
Author(s):  
G. P. MALIK
Keyword(s):  
Cooper Pair ◽  
Energy Gap ◽  
High Temperature Superconductors ◽  
Bcs Theory ◽  
Simple Extension ◽  
Cooper Pairs ◽  
Debye Temperatures ◽  
Unified Study ◽  
Interesting Candidate ◽  
Composite Superconductors

Based on the concepts of a superpropagator, multiple Debye temperatures, and equivalence of the binding energy of a Cooper pair and the BCS energy gap, the set of generalized BCS equations obtained recently via a temperature-generalized Bethe–Salpeter equation is employed for a unified study of the following composite superconductors: MgB 2, Nb 3 Sn , and YBCO. In addition, we study the Nb – Al system in which Cooper pairs as resonances have recently been reported to have been observed. Our approach seems to suggest that a simple extension of the BCS theory that accommodates the concept of Cooper pairs bound via a more than one phonon exchange mechanism may be an interesting candidate for dealing with high-temperature superconductors.

scholarly journals SIGNATURE SPLITTING IN 173W WITH TRIAXIAL PARTICLE ROTOR MODEL

2009 ◽  
Vol 18 (01) ◽  
pp. 109-122 ◽  
Author(s):  
B. QI ◽  
S. Q. ZHANG ◽  
S. Y. WANG ◽  
J. MENG
Keyword(s):  
Excellent Agreement ◽  
Degree Of Freedom ◽  
The Self ◽  
Energy Spectra ◽  
Signature Splitting ◽  
Signature Inversion ◽  
Self Consistent ◽  
Strong Competition ◽  
Intruder Orbital ◽  
Rotor Model

A particle rotor model with a quasi-neutron coupled with a triaxially deformed rotor is applied to study signature splitting for bands with intruder orbital ν7/2+[633] and nonintruder orbital ν5/2-[512] in 173 W . Excellent agreement with the observed energy spectra has been achieved for both bands. Signature splitting for band ν7/2+[633], and band ν5/2-[512] before the onset of signature inversion, is satisfactorily reproduced by introducing the γ degree of freedom. The phase and amplitude of signature splitting in band ν5/2-[512] are attributed to strong competition between 2f7/2 and 1h9/2 components. However, the self-consistent explanation of signature inversion in band ν5/2-[512] is beyond the present one quasi-neutron coupled with a triaxially deformed rotor.

scholarly journals Generalised quasilinear approximation of the helical magnetorotational instability

2016 ◽  
Vol 82 (3) ◽  
Author(s):  
Adam Child ◽  
Rainer Hollerbach ◽  
Brad Marston ◽  
Steven Tobias
Keyword(s):  
Large Scale ◽  
Statistical Simulation ◽  
The Self ◽  
Energy Spectra ◽  
Magnetorotational Instability ◽  
Self Consistent ◽  
Small Scales ◽  
Direct Statistical Simulation ◽  
Quasilinear Approximation ◽  
Better Than

Motivated by recent advances in direct statistical simulation (DSS) of astrophysical phenomena such as out-of-equilibrium jets, we perform a direct numerical simulation (DNS) of the helical magnetorotational instability (HMRI) under the generalised quasilinear approximation (GQL). This approximation generalises the quasilinear approximation (QL) to include the self-consistent interaction of large-scale modes, interpolating between fully nonlinear DNS and QL DNS whilst still remaining formally linear in the small scales. In this paper we address whether GQL can more accurately describe low-order statistics of axisymmetric HMRI when compared with QL by performing DNS under various degrees of GQL approximation. We utilise various diagnostics, such as energy spectra in addition to first and second cumulants, for calculations performed for a range of Reynolds and Hartmann numbers (describing rotation and imposed magnetic field strength respectively). We find that GQL performs significantly better than QL in describing the statistics of the HMRI even when relatively few large-scale modes are kept in the formalism. We conclude that DSS based on GQL (GCE2) will be significantly more accurate than that based on QL (CE2).

APPLICATION OF THE SEKE SELF-CONSISTENT PROJECTION OPERATOR METHOD IN THE CASE OF A DISCRETIZED ATOM-FIELD INTERACTION MODEL

1999 ◽  
Vol 13 (26) ◽  
pp. 3159-3170 ◽  
Author(s):  
J. SEKE ◽  
A. V. SOLDATOV ◽  
N. N. BOGOLUBOV
Keyword(s):  
Quantum Optics ◽  
Projection Operator ◽  
Interaction Model ◽  
Operator Method ◽  
Continuous Limit ◽  
Relaxation Dynamics ◽  
Field Interaction ◽  
Projection Operator Method ◽  
Self Consistent ◽  
Irreversible Dynamics

The relaxation dynamics in the case of a discretized atom-field interaction model, being of great importance in quantum optics, is investigated numerically by an algorithm based on Seke's self-consistent projection operator method. The transition from reversible to irreversible dynamics in the continuous limit is simulated numerically. The dependence of the time evolution of atomic nondecay probability on the number of discrete-field modes, coupled to the atom, is discussed.

GENERALIZED BOSE-EINSTEIN CONDENSATION IN SUPERCONDUCTIVITY

2010 ◽  
Vol 24 (25n26) ◽  
pp. 5163-5171
Author(s):  
MANUEL de LLANO
Keyword(s):  
Spin Fluctuation ◽  
Interaction Model ◽  
Bcs Theory ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Condensation Energy ◽  
Weakly Bound ◽  
Bose Einstein Condensation ◽  
Fermi Temperature ◽  
Bose Einstein

Unification of the BCS and the Bose-Einstein condensation (BEC) theories is surveyed in detail via a generalized BEC (GBEC) finite-temperature statistical formalism. Its major difference with BCS theory is that it can be diagonalized exactly. Under specified conditions it yields the precise BCS gap equation for all temperatures as well as the precise BCS zero-temperature condensation energy for all couplings, thereby suggesting that a BCS condensate is a BE condensate in a ternary mixture of kinematically independent unpaired electrons coexisting with equally proportioned weakly-bound two-electron and two-hole Cooper pairs. Without abandoning the electron-phonon mechanism in moderately weak coupling it suffices, in principle, to reproduce the unusually high values of Tc (in units of the Fermi temperature TF) of 0.01-0.05 empirically reported in the so-called "exotic" superconductors of the Uemura plot, including cuprates, in contrast to the low values of Tc/TF ≤ 10-3 roughly reproduced by BCS theory for conventional (mostly elemental) superconductors. Replacing the characteristic phonon-exchange Debye temperature by a characteristic magnon-exchange one more than twice in size can lead to a simple interaction model associated with spin-fluctuation-mediated pairing.

scholarly journals ABSENCE OF BCS CONDENSATION OF ATOMS IN A REPULSIVE FERMI GAS OF ATOMS

2008 ◽  
Vol 22 (01) ◽  
pp. 9-16
Author(s):  
FUXIANG HAN ◽  
HAILING LI ◽  
MINGHAO LEI ◽  
E. WU
Keyword(s):  
Fermi Gas ◽  
Order Parameters ◽  
The Self ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Path Integral Representation ◽  
Body Interaction ◽  
Self Consistent ◽  
Atom Interaction ◽  
Bose Einstein

Bose–Einstein condensation of molecules and BCS condensation of Cooper pairs of atoms in an ultra-cold Fermi gas of atoms with a repulsive two-body interaction are studied by using the path integral representation of the grand partition function. From the self-consistent equations obtained in the present work for the order parameters, we have found that BCS condensation of atoms cannot occur in such a Fermi gas of atoms and that the condensate observed experimentally is composed of condensed molecules or possibly of preformed Cooper pairs. To substantiate our conclusions from the self-consistent equations for the order parameters, the effective atom–atom interaction mediated through molecules has also been computed with the Foldy–Wouthuysen transformation and has been found to be repulsive, which implies a net repulsive two-body interaction between atoms and hence the absence of BCS condensation of atoms.

Electronic Structure of Pd doped InP

1992 ◽  
Vol 272 ◽  
Author(s):  
P. K. Khowash
Keyword(s):  
Electronic Structure ◽  
Density Of States ◽  
Cluster Model ◽  
Local Density ◽  
Energy Spectra ◽  
Valence Band Edge ◽  
Metal Impurities ◽  
Structure Of Metal ◽  
Self Consistent ◽  
Small Magnetic Moment

ABSTRACTThe electronic structure of metal impurities in III-V semiconductors are interesting because of their ability to create deep centers. We use a spin unrestricted self-consistent local density theory in a cluster model to calculate the charge distributions, one electron energy spectra and the density of states for pure InP and Pd doped InP, substituted at the In site. The pure semiconductor gap is calculated to be 1.44 eV in excellent agreement with the experimental value of 1.41 eV. A small magnetic moment of 0.561μB appears on the Pd site. The impurity introduces a levels of t2 character at 0.01 and 0.04 eV above the valence band edge.

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