4,029 research outputs found
The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/d-wave superconductor contact
The influence of phase shifts of electron waves passing through and reflected
by the potential barrier on the Andreev reflection in a
ferromagnet/isolator/d-wave superconductor (FIS) contact is studied. It is
found that in a superconductor the surface spin-dependent Andreev bound states
inside the superconducting gap are formed as a result of the interference of
electron-like and hole-like quasiparticles due to repeated Andreev reflections.
The peak in the conductance of the FIS contact at the zero potential for the
(110)-oriented superconductor disappears rapidly as the polarization of a
ferromagnet increases, whereas for the (100)-oriented superconductor it
appears. The physical reason for this behavior of conductance is discussed.Comment: 8 pages, 4 figure
Contributions of spontaneous phase slippage to linear and non-linear conduction near the Peierls transition in thin samples of o-TaS_3
In the Peierls state very thin samples of TaS_3 (cross-section area \sim
10^{-3} mkm^2) are found to demonstrate smearing of the I-V curves near the
threshold field. With approaching the Peierls transition temperature, T_P, the
smearing evolves into smooth growth of conductance from zero voltage
interpreted by us as the contribution of fluctuations to the non--linear
conductance. We identify independently the fluctuation contribution to the
linear conductance near T_P. Both linear and non-linear contributions depend on
temperature with close activation energies \sim (2 - 4) x 10^3 K and apparently
reveal the same process. We reject creep of the {\it continuous} charge-density
waves (CDWs) as the origin of this effect and show that it is spontaneous phase
slippage that results in creep of the CDW. A model is proposed accounting for
both the linear and non-linear parts of the fluctuation conduction up to T_P.Comment: 6 pages, 5 Postscript figure, RevTeX, accepted for publication in PR
NN potentials from inverse scattering in the J-matrix approach
An approximate inverse scattering method [7,8] has been used to construct
separable potentials with the Laguerre form factors. As an application, we
invert the phase shifts of proton-proton in the and
channels and neutron-proton in the channel elastic scattering. In
the latter case the deuteron wave function of a realistic potential was
used as input.Comment: LaTex2e, 17 pages, 3 Postscript figures; corrected typo
Local thermometry technique based on proximity-coupled superconductor/normal-metal/superconductor devices
In mesoscopic superconductor/normal-metal/superconductor (SNS)
heterostructures, it is known that the resistance of the normal metal between
the superconductors has a strong temperature dependence. Based on this
phenomenon, we have developed a new type of thermometer, which dramatically
enhances our ability to measure the local electron temperature Te at low
temperatures. Using this technique, we have been able to measure small
temperature gradients across a micron-size sample, opening up the possibility
of quantitatively measuring the thermal properties of mesoscopic devices.Comment: 4 pages, 4 figure
Transport and triplet superconducting condensate in mesoscopic ferromagnet-superconductor structures
We calculate the conductance of a superconductor/ferromagnet (S/F) mesoscopic
structure in the dirty limit. First we assume that the ferromagnet exhibits a
homogeneous magnetization and consider the case that the penetration of the
condensate into the F wire is negligible and the case in which the proximity
effect is taken into account. It is shown that if the exchange field is large
enough, the conductance below the critical temperature , is always smaller
than the conductance in the normal state. At last, we calculate the conductance
for a F/S structure with a local inhomogeneity of the magnetization in the
ferromagnet. We demonstrate that a triplet component of the condensate is
induced in the F wire.This leads to a increase of the conductance below .Comment: 31 pages, 6 figures. to be published in International Journal of
Modern Physics B; references adde
Superradiance from an ultrathin film of three-level V-type atoms: Interplay between splitting, quantum coherence and local-field effects
We carry out a theoretical study of the collective spontaneous emission
(superradiance) from an ultrathin film comprised of three-level atoms with
-configuration of the operating transitions. As the thickness of the system
is small compared to the emission wavelength inside the film, the local-field
correction to the averaged Maxwell field is relevant. We show that the
interplay between the low-frequency quantum coherence within the subspace of
the upper doublet states and the local-field correction may drastically affect
the branching ratio of the operating transitions. This effect may be used for
controlling the emission process by varying the doublet splitting and the
amount of low-frequency coherence.Comment: 15 pages, 5 figure
Observation of the second harmonic in superconducting current-phase relation of Nb/Au/(001)YBa2Cu3Ox heterojunctions
The superconducting current-phase relation (CPR) of Nb/Au/(001)YBa2Cu3Ox
heterojunctions prepared on epitaxial c-axis oriented YBa2Cu3Ox thin films has
been measured in a single-junction interferometer. For the first time, the
second harmonic of the CPR of such junctions has been observed. The appearance
of the second harmonic and the relative sign of the first and second harmonics
of the CPR can be explained assuming, that the macroscopic pairing symmetry of
our YBa2Cu3Ox thin films is of the d+s typeComment: 11 pages, 4 figure
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