122 research outputs found
Electronic spectrum and tunnelling properties of multi-wall carbon nanotubes
We develop a general approach to calculations of the electron spectrum of
metallic multi-wall carbon nanotubes (MWNT) with arbitrary number of coaxial
layers. It is based on the model with singular attractive potential of
equidistant conductive cylinders. The knowledge of one-electron spectrum allows
to construct the corresponding Green function and then to calculate the entropy
and density of states for MWNT. We analyze the tunnelling between the nanotube
and normal metal electrode. The possibility of direct determination of
one-electron density of states by measurements of the tunnelling conductivity
at low temperatures is proved and the necessary restrictions on temperature are
formulated. We discuss briefly the conflicting experimental observations of
electronic properties of MWNT.Comment: 14 pages, 1 figur
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
Superconducting fluctuation corrections to ultrasound attenuation in layered superconductors
We consider the temperature dependence of the sound attenuation and sound
velocity in layered impure metals due to superconducting fluctuations of the
order parameter above the critical temperature. We obtain the dependence on
material properties of these fluctuation corrections in the hydrodynamic limit,
where the electron mean free path is much smaller than the wavelength of sound
and where the electron collision rate is much larger than the sound frequency.
For longitudinal sound propagating perpendicular to the layers, the open Fermi
surface condition leads to a suppression of the divergent contributions to
leading order, in contrast with the case of paraconductivity. The leading
temperature dependent corrections, given by the Aslamazov-Larkin, Maki-Thompson
and density of states terms, remain finite as T->Tc. Nevertheless, the
sensitivity of new ultrasonic experiments on layered organic conductors should
make these fluctuations effects measurable.Comment: 13 pages, 6 figures. Accepted for PRB. Added discussion on incoherent
interlayer tunneling and other small modifications suggested by referee
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