793 research outputs found
Fluctuation spectroscopy of granularity in superconducting structures
We suggest to use `fluctuation spectroscopy' as a method to detect
granularity in a disordered metal close to a superconducting transition. We
show that with lowering temperature the resistance of a system of
relatively large grains initially grows due to the fluctuation suppression of
the one-electron tunneling but decreases with further lowering due to the
coherent charge transfer of the fluctuation Cooper pairs. Under certain
conditions, such a maximum in turns out to be sensitive to weak magnetic
fields due to a novel Maki -- Thompson type mechanism.Comment: A final version, as published; the introduction and summary are
considerably revise
Space-time dispersion of graphene conductivity
We present an analytic calculation of the conductivity of pure graphene as a
function of frequency , wave-vector , and temperature for the range
where the energies related to all these parameters are small in comparison with
the band parameter eV. The simple asymptotic expressions are given
in various limiting cases. For instance, the conductivity for is equal to and independent of the
band structure parameters and . Our results are also used to
explain the known dependence of the graphite conductivity on temperature and
pressure.Comment: 4 pages, 1 figure, to be submitte
How the Phase Slips in a Current-Biased Narrow Superconducting Stripe?
The theory of current transport in a narrow superconducting channel
accounting for thermal fluctuations is revisited. The value of voltage
appearing in the sample is found as the function of temperature (close to
transition temperature ) and bias
current ( is a value of critical current
calculated in the framework of the BCS approximation, neglecting thermal
fluctuations). It is shown that the careful analysis of vortex crossing of the
stripe results in considerable increase of the activation energy.Comment: 6 pages, 2 figure
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
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