502 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
Quantum Fluctuations and Dynamic Clustering of Fluctuating Cooper Pairs
We derive exact expressions for the fluctuation conductivity in two
dimensional superconductors as a function of temperature and magnetic field in
the whole fluctuation region above the upper critical field H_{c2}(T). Focusing
on the vicinity of the quantum phase transition near zero temperature, we
propose that as the magnetic field approaches the line near H_{c2}(0) from
above, a peculiar dynamic state consisting of clusters of coherently rotating
fluctuation Cooper-pairs forms and estimate the characteristic size and
lifetime of such clusters. We find the zero temperature magnetic field
dependence of the the transverse magnetoconductivity above H_{c2}(0) in layered
superconductors.Comment: 5 pages, 3 figure
Quantization of entropy in a quasi-two-dimensional electron gas
We demonstrate that the partial entropy of a two-dimensional electron gas
(2DEG) exhibits quantized peaks at resonances between the chemical potential
and electron levels of size quantization. In the limit of no scattering, the
peaks depend only on the subband quantization number and are independent on
material parameters, shape of the confining potential, electron effective mass
and temperature. The quantization of partial entropy is a signature of a
topological phase transition in a 2DEG. In the presence of stationary disorder,
the magnitude of peaks decreases. Its deviation from the quantized values is a
direct measure of the disorder induced smearing of the electronic density of
states.Comment: 4 pages, 2 figure
Spherical functions on the de Sitter group
Matrix elements and spherical functions of irreducible representations of the
de Sitter group are studied on the various homogeneous spaces of this group. It
is shown that a universal covering of the de Sitter group gives rise to
quaternion Euler angles. An explicit form of Casimir and Laplace-Beltrami
operators on the homogeneous spaces is given. Different expressions of the
matrix elements and spherical functions are given in terms of multiple
hypergeometric functions both for finite-dimensional and unitary
representations of the principal series of the de Sitter group.Comment: 40 page
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