197 research outputs found
Vitaly Ginzburg and High Temperature Superconductivity: Personal Reminiscences
I offer some personal reminiscences from the period of 1976-1983, when I was
a M. Sc. and then a Ph.D. student in Vitaly L. Ginzburg's High Temperature
Superconductivity group at the P.N. Lebedev Institute in MoscowComment: To be published in proceedings of the Notre Dame Workshop on the
Possibility of Room Temperature Superconductivity, June 2005 v.2: an apposite
epigraph adde
Fluctuations in superconducting rings with two order parameters
Starting from the Ginzburg-Landau energy functional, we discuss how the
presence of two order parameters and the coupling between them influence a
superconducting ring in the fluctuative regime. Our method is exact, but
requires numerical implementation. We also study approximations for which some
analytic expressions can be obtained, and check their ranges of validity. We
provide estimates for the temperature ranges where fluctuations are important,
calculate the persistent current in magnesium diboride rings as a function of
temperature and enclosed flux, and point out its additional dependence on the
cross-section area of the ring. We find temperature regions in which
fluctuations enhance the persistent currents and regions where they inhibit the
persistent current. The presence of two order parameters that can fluctuate
independently always leads to larger averages of the order parameters at Tc,
but only for appropriate parameters this yields larger persistent current. In
cases of very different material parameters for the two coupled condensates,
the persistent current is inhibited
Intercalant-Driven Superconductivity in YbC and CaC
Recently deiscovered superconductivity in YbC and CaC at temperatures
substantially higher than previously known for intercalated graphites, raised
several new questions: (1) Is the mechanism considerably different from the
previously known intercalated graphites? (2) If superconductivity is
conventional, what are the relevant phonons? (3) Given extreme similarity
between YbC and CaCa, why their critical temperatures are so different?
We address these questions on the basis of first-principles calculations and
conclude that coupling with intercalant phonons is likely to be the main force
for superconductivity in YbC and CaC, but not in alkaline-intercalated
compounds, and explain the difference in by the ``isotope effect'' due to
the difference in Yb and Ca atomic masses.Comment: 4 pages, embedded postscript figire
Is the term "type-1.5 superconductivity" warranted by Ginzburg-Landau theory?
It is shown that within the Ginzburg-Landau (GL) approximation the order
parameters Delta1(r, T) and Delta2(r, T) in two-band superconductors vary on
the same length scale, the difference in the zero-T coherence lengths xi0_i
~vF_i/Delta_i(0), i = 1, 2 notwithstanding. This amounts to a single physical
GL parameter kappa and the classic GL dichotomy: kappa < 1/sqrt(2) for type-I
and kappa > 1/sqrt(2) for type-II.Comment: 5 pages, revised and extended version; previous title "Two-band
superconductors near Tc" change
Leduc-Righi effect in superconductors with nontrivial density of states
Increasing of electronic thermal conductivity of superconductor in the model
with nontrivial density of states was considered. The electronic thermal
conductivity K(T) of SC in the presence of external magnetic field was
investigated. It was shown that if symmetrical part of quasiparticle scattering
rate less than cyclotron energy observed mechanism of increasing K(T) can be
separated from connected with asymmetric electronic scattering effects another
one.Comment: 5 pages, RevTe
NMR relaxation time in a clean two-band superconductor
We study the spin-lattice relaxation rate of nuclear magnetic resonance in a
two-band superconductor. Both conventional and unconventional pairing
symmetries for an arbitrary band structure in the clean limit are considered.
The importance of the inter-band interference effects is emphasized. The
calculations in the conventional case with two isotropic gaps are performed
using a two-band generalization of Eliashberg theory.Comment: 9 pages, 3 figure
Electron-lattice interaction and its impact on high Tc superconductivity
In this Colloquium, the main features of the electron-lattice interaction are
discussed and high values of the critical temperature up to room temperature
could be provided. While the issue of the mechanism of superconductivity in the
high Tc cuprates continues to be controversial, one can state that there have
been many experimental results demonstrating that the lattice makes a strong
impact on the pairing of electrons. The polaronic nature of the carriers is
also a manifestation of strong electron-lattice interaction. One can propose an
experiment that allows an unambiguous determination of the intermediate boson
(phonon, magnon, exciton, etc.) which provides the pairing. The
electron-lattice interaction increases for nanosystems, and this is due to an
effective increase in the density of states
Effect of electron-phonon interaction on the shift and attenuation of optical phonons
Using the Boltzmann equation for electrons in metals, we show that the
optical phonons soften and have a dispersion due to screening in agreement with
the results reported recently [M. Reizer, Phys. Rev. B {\bf 61}, 40 (2000)].
Additional phonon damping and frequency shift arise when the electron--phonon
interaction is properly included.Comment: 4 pages, late
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