100 research outputs found
Thermal transport in granular metals
We study the electron thermal transport in granular metals at large tunnel
conductance between the grains, and not too low a temperature , where is the mean energy level spacing for a single grain.
Taking into account the electron-electron interaction effects we calculate the
thermal conductivity and show that the Wiedemann-Franz law is violated for
granular metals. We find that interaction effects suppress the thermal
conductivity less than the electrical conductivity.Comment: Replaced with published versio
Superconducting fluctuations at low temperature
The effect of fluctuations on the transport and thermodynamic properties of
two-dimensional superconductors in a magnetic field is studied at low
temperature. The fluctuation conductivity is calculated in the framework of the
perturbation theory with the help of usual diagram technique. It is shown that
in the dirty case the Aslamazov-Larkin, Maki-Thomson and Density of States
contributions are of the same order. At extremely low temperature, the total
fluctuation correction to the normal conductivity is negative in the dirty
limit and depends on the external magnetic field logarithmically. In the
non-local clean limit, the Aslamazov-Larkin contribution to conductivity is
evaluated with the aid of the Helfand-Werthamer theory. The longitudinal and
Hall conductivities are found. The fluctuating magnetization is calculated in
the one-loop and two-loop approximations.Comment: 12 pages, 4 figures, submitted to Phys. Rev.
Interaction corrections to the thermal transport coefficients in disordered metals: quantum kinetic equation approach
We consider the singular electron-electron interaction corrections to the
transport coefficients in disordered metals to test the validity of the
Wiedemann-Franz law. We develop a local, quantum kinetic equation approach in
which the charge and energy conservation laws are explicitly obeyed. To obtain
the local description, we introduce bosonic distribution functions for the
neutral, low-energy collective modes (electron-hole pairs). The resulting
system of kinetic equations enables us to distinguish between the different
physical processes involved in the charge and energy transport: elastic
electron scattering affects both, while the inelastic processes influence only
the latter. Moreover, the neutral bosons, though incapable of transporting
charge, contribute significantly to the energy transport. In our approach we
calculate on equal footing the electrical and thermal conductivities and the
specific heat in any dimension. We found that the Wiedemann-Franz law is always
violated by the interaction corrections; the violation is larger for one- and
two-dimensional systems in the diffusive regime and it is due
to the energy transported by the neutral bosons. For two-dimensional systems in
the quasi-ballistic regime the inelastic scattering of the
electron on the bosons also contributes to the violation.Comment: 4 figures, 35 page
Quasiparticle contribution to heat carriers relaxation time in DyBaCuO from heat diffusivity measurements
It is shown that the controversy on phonons or electrons being the most
influenced heat carriers below the critical temperature of high-T
superconductors can be resolved. Electrical and thermal properties of the same
DyBaCuO monodomain have been measured for two highly different
oxygenation levels. While the oxygenated sample DyBaCuO has very
good superconducting properties ( K), the DyBaCuO
sample exhibits an insulator behavior. A careful comparison between
measurements of the {\bf thermal diffusivity} of both samples allows us to
extract the electronic contribution. This contribution to the relaxation time
of heat carriers is shown to be large below and more sensitive to the
superconducting state than the phonon contribution.Comment: 13 pages, 6 figure
Effects of proximity to an electronic topological transition on normal state transport properties of the high-Tc superconductors
Within the time dependent Ginzburg-Landau theory, the effects of the
superconducting fluctuations on the transport properties above the critical
temperature are characterized by a non-zero imaginary part of the relaxation
rate gamma of the order parameter. Here, we evaluate Im gamma for an
anisotropic dispersion relation typical of the high-Tc cuprate superconductors
(HTS), characterized by a proximity to an electronic topological transition
(ETT). We find that Im gamma abruptly changes sign at the ETT as a function of
doping, in agreement with the universal behavior of the HTS. We also find that
an increase of the in-plane anisotropy, as is given by a non-zero value of the
next-nearest to nearest hopping ratio r=t'/t, increases the value of | Im gamma
| close to the ETT, as well as its singular behavior at low temperature,
therefore enhancing the effect of superconducting fluctuations. Such a result
is in qualitative agreement with the available data for the excess Hall
conductivity for several cuprates and cuprate superlattices.Comment: to appear in Phys. Rev.
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