37 research outputs found
Proximity and Josephson effects in superconductor - two dimensional electron gas planar junctions
The DC Josephson effect is theoretically studied in a planar junction in
which a two dimensional electron gas (2DEG) infinite in lateral directions is
in contact with two superconducting electrodes placed on top of the 2DEG. An
energy gap in the excitation spectrum is created in the 2DEG due to the
proximity effect. It is shown that under certain conditions, the region of the
2DEG underneath the superconductors is analogous to a superconducting region
with an order parameter \/, where
\/ depends on the interface transmittance
and the Fermi velocity mismatch between the superconductors and the 2DEG.Comment: 9 pages REVTeX, 5 figures available on reques
Experimental determination of the quasi-particle decay length in a superconducting quantum well
We have investigated experimentally the electronic transport properties of a
two-dimensional electron gas (2DEG) present in an AlSb/InAs/AlSb quantum well,
where part of the toplayer has been replaced by a superconducting Nb strip,
with an energy gap . By measuring the lateral electronic transport
underneath the superconductor, and comparing the experimental results with a
model based on the Bogoliubov-de Gennes equation and the Landauer-B\"uttiker
formalism, we obtain a decay length for
electrons. This decay length corresponds to an interface transparency
between the Nb and InAs. Using this value, we infer an
energy gap in the excitation spectrum of the SQW of .Comment: Revtex, 3 PostScript figure
Extraordinary Temperature Dependence of the Resonant Andreev Reflection
An extraordinary temperature dependence of the resonant Andreev reflection
via discrete energy level in a normal-metal / quantum-dot / superconductor
(N-QD-S) system is predicted theoretically by using Green function technique.
The width of zero bias conductance peak in N-QD-S is about and does not exhibit thermal broadening, where and
are the coupling strength between QD and leads. Considering the
intra-dot Coulomb interaction, the Coulomb blockade oscillations conducted by
Andreev reflection differs dramatically from that in N-QD-N. Instead of thermal
broadening, finite temperature induces more resonant peaks around the
oscillation peaks of zero temperature. This effect can be applied to determine
the coupling strength and QD level spacing in N-QD-S.Comment: 11 pages, 3 figures, LaTe
Nonlinearity in NS transport: scattering matrix approach
A general formula for the current through a disordered
normal--superconducting junction is derived, which is valid at finite
temperature and includes the full voltage dependence. The result depends on a
multichannel scattering matrix, which describes elastic scattering in the
normal region, and accounts for the Andreev scattering at the NS interface. The
symmetry of the current with respect to sign reversal in the subgap regime is
discussed. The Andreev approximation is used to derive a spectral conductance
formula, which applies to voltages both below and above the gap. In a case
study the spectral conductance formula is applied to the problem of an NINIS
double barrier junction.Comment: 26 pages, 4 Postscript figures, Latex, to be published in Phys. Rev.
Mesoscopic proximity effect in double barrier Superconductor/Normal Metal junctions
We report transport measurements down to T=60mK of SININ and SNIN structures
in the diffusive limit. We fabricated Al-AlOx/Cu/AlOx/Cu (SININ) and
Al/Cu/AlOx/Cu (SNIN) vertical junctions. For the first time, a zero bias
anomaly was observed in a metallic SININ structure. We attribute this peak of
conductance to coherent multi-reflections of electrons between the two tunnel
barriers. This conductance maximum is quantitatively fitted by the relevant
theory of mesoscopic SININ structures. When the barrier at the SN interface is
removed (SNIN structure), we observe a peak of conductance at finite voltage
accompagnied by an excess of sub-gap conductance.Comment: 4 pages, 4 figures, editorially approved for publication in Phys.
Rev. B Rapid Com
Evidence of two-electron tunneling interference in Nb/InAs junctions
The impact of junction transparency in driving phase-coherent charge transfer
across diffusive semiconductor-superconductor junctions is demonstrated. We
present conductivity data for a set of Nb-InAs junctions differing only in
interface transparency. Our experimental findings are analyzed within the
quasi-classical Green-function approach and unambiguously show the physical
processes giving rise to the observed excess zero-bias conductivity.Comment: 10 pages (RevTex), 4 figures (PostScript), accepted for pubblication
in Physical Review
Effect of transport-induced charge inhomogeneity on point-contact Andreev reflection spectra at ferromagnet-superconductor interfaces
We investigate the transport properties of a ferromagnet-superconductor
interface within the framework of a modified three-dimensional
Blonder-Tinkham-Klapwijk formalism. In particular, we propose that charge
inhomogeneity forms via two unique transport mechanisms, namely, evanescent
Andreev reflection and evanescent quasiparticle transmission. Furthermore, we
take into account the influence of charge inhomogeneity on the interfacial
barrier potential and calculate the conductance as a function of bias voltage.
Point-contact Andreev reflection (PCAR) spectra often show dip structures,
large zero-bias conductance enhancement, and additional zero-bias conductance
peak. Our results indicate that transport-induced charge inhomogeneity could be
a source of all these anomalous characteristics of the PCAR spectra.Comment: 9 pages, 6 figure