10,828 research outputs found
Effect of electron corelation on superconducting pairing symmetry
The role of electron correlation on different pairing symmetries are
discussed in details where the electron correlation has been treated within the
slave boson formalism. It is shown that for a pure or pure wave pairing
symmetry, the electronic correlation suppresses the wave gap magnitude (as
well as the ) at a faster rate than that for the wave gap. On the
otherhand, a complex order parameter of the form () shows anomalous
temperature dependence. For example, if the temperature () at which
the wave component of the complex order parameter vanishes happens to be
larger than that for the wave component () then the growth of the
wave component is arrested with the onset of the wave component of the
order parameter. In this mixed phase however, we find that the suppression in
different components of the gap as well as the corresponding due to
coulomb correlation are very sensitive to the relative pairing strengths of
and channels as well as the underlying lattice. Interestingly enough, in
such a scenario (for a case of ) the gap magnitude of the
wave component increases with electron correlation but not for
certain values of electron correlation. However, this never happens in case of
the wave component. We also calculate the temperature dependence of the
superconducting gap along both the high symmetry directions ( - M and
- X) in a mixed symmetry pairing state and the thermal
variation of the gap anisotropy () with electron correlation. The results are discussed with reference to
experimental observations.Comment: 22 pages, latex, 12 figures (attached in ps /eps) Journal : Accepted
for publication in Euro. J. Phys
Investigation of Complex Impedance and Modulus Properties of Nd Doped 0.5BiFeO3-0.5PbTiO3 Multiferroic Composites
0.5BiNdxFe1-xO3-0.5PbTiO3 (x=0.05, 0.10, 0.15, 0.20) composites were
successfully synthesized by a solid state reaction technique. At room
temperature X-ray diffraction shows tetragonal structure for all concentrations
of Nd doped 0.5BiFeO3-0.5PbTiO3 composites. The nature of Nyquist plot confirms
the presence of bulk effects only for all compositions of Nd-doped
0.5BiFeO3-0.5PbTiO3 composites. The bulk resistance is found to decreases with
the increasing in temperature as well as Nd concentration and exhibits a
typical negative temperature coefficient of resistance (NTCR) behavior. Both
the complex impedance and modulus studies have suggested the presence of
non-Debye type of relaxation in the materials. Conductivity spectra reveal the
presence of hopping mechanism in the electrical transport process of the
materials. The activation energy of the composite increases with increasing Nd
concentration and were found to be 0.28, 0.27, 0.31 and 0.32eV for x=0.05,
0.10, 0.15, 0.20 respectively at 200-275 oC for conduction process.Comment: 22 pages, 12 figures, 2 tables, 34 Referenc
Anti-isospectral Transformations, Orthogonal Polynomials and Quasi-Exactly Solvable Problems
We consider the double sinh-Gordon potential which is a quasi-exactly
solvable problem and show that in this case one has two sets of Bender-Dunne
orthogonal polynomials . We study in some detail the various properties of
these polynomials and the corresponding quotient polynomials. In particular, we
show that the weight functions for these polynomials are not always positive.
We also study the orthogonal polynomials of the double sine-Gordon potential
which is related to the double sinh-Gordon case by an anti-isospectral
transformation. Finally we discover a new quasi-exactly solvable problem by
making use of the anti-isospectral transformation.Comment: Revtex, 19 pages, No figur
Relaxation of Collective Excitations in LJ-13 Cluster
We have performed classical molecular dynamics simulation of
cluster to study the behavior of collective excitations. In the solid ``phase''
of the cluster, the collective oscillation of the monopole mode can be well
fitted to a damped harmonic oscillator. The parameters of the equivalent damped
harmonic oscillator-- the damping coefficient, spring constant, time period of
oscillation and the mass of the oscillator -- all show a sharp change in
behavior at a kinetic temperature of about . This marks yet another
characteristic temperature of the system, a temperature below which
collective excitations are very stable, and at higher temperatures the single
particle excitations cause the damping of the collective oscillations. We argue
that so long as the cluster remains confined within the global potential energy
minimum the collective excitations do not decay; and once the cluster comes out
of this well, the local potential energy minima pockets act as single particle
excitation channels in destroying the collective motion. The effect is manifest
in almost all the physical observables of the cluster.Comment: Revised and enlarged. 6 pages RevTeX style. 7 eps figures available
on request. To appear in J Chem Phy
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