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Дата изменения: Thu Sep 1 13:25:15 2005 Дата индексирования: Tue Oct 2 03:55:58 2012 Кодировка: Поисковые слова: trees |
Supported by: | Russian Foundation for Basic Research, Project number 04-02-16818 |
Duration: | 2004-2006 |
Supervisor: | Karen Constantinian, IREE RAS, Moscow, Russia |
Theoretical investigation was carried out of electron transport phenomena in
superconducting heterostructures S-MB-N and S-MB-S with magnetic barriers (MB)
determined by monolayer of ferromagnet (F) or spin-valve structures FNF or FIF
(N is a normal metal, I is insulating layer). The I-V characteristics of S-MB-N
structures were found for voltages including DC and AC (oscillating with
definite frequency) components. The DC Josephson effect was studied for S-FIF-S
and S-FcF-S structures (c is a constriction) for diffusive transport through F
layers with arbitrary mutual orientation of the exchange fields (EF) in the F
layers directed parallel to their planes. For these structures the theory of AC
Josephson effect was constructed for the cases of parallel and antiparallel EF
orientations in the F layers.
The I-V characteristics of cuprate bicrystal Josephson junctions have been
experimentally investigated at different temperatures, barrier transparency
factors and the phase difference of superconducting electrodes. Experimental
data testify, that the most probable mechanism of current transport in such
structures is a tunneling through a barrier with participation in the process of
the mid-gap bound states, arising from multiple Andreev reflection. However no
complete theory exists, which can explain experimental situation: deviations of
waveforms of current-phase relation and magnetic-field dependences of a critical
current, features caused by non-homogeneous barrier nature, arising from barrier
faceting during the epitaxial film growth.
For bicrystal junctions with d-wave superconducting electrodes at high voltages
V> 5 mV an excess noise larger than thermal fluctuations have been observed,
conterminous with the dependence of shot noise as for the case of
superconducting SIS tunnel junctions. In the region of small voltages V <1 mV
such junctions show peak of noise (excess over 2e of effective transferred
charge), a characteristic, inherent to superconducting junctions with multiple
Andreev reflection.
In planar heterojunctions Nb/Au/YBa2Cu3Ox with an inclined c-axis of the
YBa2Cu3Ox film a reduction of the maximal height of the first Shapiro step with
increase of applied microwave frequency was revealed. Observation of the
sub-harmonic detector response and the fractional n=1/2 Shapiro steps are
specific for the presence of the second harmonic in current-phase relation.
The novel type of thin-film bicrystal Josephson junctions made from metal-oxide
superconductors with the asymmetrically inclined electrode is offered and
fabricated. The first investigations of electron transport and dynamic microwave
characteristics of those junctions have been carried out.