256 research outputs found
Shot noise of large charge quanta in superconductor/semiconductor/superconductor junctions
We have found experimentally that the noise of ballistic electron transport
in a superconductor/semiconductor/superconductor junction is enhanced relative
to the value given by the general relation, S_V=2eIR^2coth(eV/2kT), for two
voltage regions in which this expression reduces to its thermal and shot noise
limits. The noise enhancement is explained by the presence of large charge
quanta, with effective charge q*=(1+2Delta/eV)e, that generate a noise spectrum
S_V=2q*IR^2, as predicted in Phys. Rev. Lett. 76, 3814 (1996). These charge
quanta result from multiple Andreev reflections at each junction interface,
which are also responsible for the subharmonic gap structure observed in the
voltage dependence of the junction's conductance.Comment: 5 pages, 5 figures, submitted to Physical Review B as a Rapid
Communication. v2 author name in reference corrected. v3 added references. v4
clarifications in the text and reference added thanks to C. Urbin
Controlling spin in an electronic interferometer with spin-active interfaces
We consider electronic current transport through a ballistic one-dimensional
quantum wire connected to two ferromagnetic leads. We study the effects of the
spin-dependence of interfacial phase shifts (SDIPS) acquired by electrons upon
scattering at the boundaries of the wire. The SDIPS produces a spin splitting
of the wire resonant energies which is tunable with the gate voltage and the
angle between the ferromagnetic polarizations. This property could be used for
manipulating spins. In particular, it leads to a giant magnetoresistance effect
with a sign tunable with the gate voltage and the magnetic field applied to the
wire.Comment: 5 pages, 3 figures. to be published in Europhysics Letter
Weak antilocalization in a polarization-doped AlxGa1-xN/GaN heterostructure with single subband occupation
Spin-orbit scattering in a polarization-doped Al0.30Ga0.70N/GaN two-dimensional electron gas with one occupied subband is studied at low temperatures. At low magnetic fields weak antilocalization is observed, which proves that spin-orbit scattering occurs in the two-dimensional electron gas. From measurements at various temperatures the elastic scattering time tau(tr), the dephasing time tau(phi), and the spin-orbit scattering time tau(so) are extracted. Measurements in tilted magnetic fields were performed, in order to separate spin and orbital effects
Doppler Shift in Andreev Reflection from a Moving Superconducting Condensate in Nb/InAs Josephson Junctions
We study narrow ballistic Josephson weak links in a InAs quantum wells
contacted by Nb electrodes and find a dramatic magnetic-field suppression of
the Andreev reflection amplitude, which occurs even for in-plane field
orientation with essentially no magnetic flux through the junction. Our
observations demonstrate the presence of a Doppler shift in the energy of the
Andreev levels, which results from diamagnetic screening currents in the hybrid
Nb/InAs-banks. The data for conductance, excess and critical currents can be
consistently explained in terms of the sample geometry and the McMillan energy,
characterizing the transparency of the Nb/InAs-interface.Comment: 4 pages, 5 figures, title modifie
Andreev reflection at high magnetic fields: Evidence for electron and hole transport in edge states
We have studied magnetotransport in arrays of niobium filled grooves in an
InAs/AlGaSb heterostructure. The critical field of up to 2.6 T permits to enter
the quantum Hall regime. In the superconducting state, we observe strong
magnetoresistance oscillations, whose amplitude exceeds the Shubnikov-de Haas
oscillations by a factor of about two, when normalized to the background.
Additionally, we find that above a geometry-dependent magnetic field value the
sample in the superconducting state has a higher longitudinal resistance than
in the normal state. Both observations can be explained with edge channels
populated with electrons and Andreev reflected holes.Comment: accepted for Phys Rev Lett, some changes to tex
Особенности химизма блеклых руд участка ЭМИ Светлинского эпитермального рудного поля (Хабаровский край)
We experimentally studied the Josephson supercurrent in Nb/InN-nanowire/Nb junctions. Large
critical currents up to 5.7 μA have been achieved, which proves the good coupling of the nanowire
to the superconductor. The effect of a magnetic field perpendicular to the plane of the Josephson
junction on the critical current has been studied. The observed monotonous decrease in the critical
current with magnetic field is explained by the magnetic pair-breaking effect in planar Josephson
junctions of ultra-narrow width [J. C. Cuevas and F. S. Bergeret, Phys. Rev. Lett. 99, 217002 (2007)]
Longitudinal photocurrent spectroscopy of a single GaAs/AlGaAs v-groove quantum wire
Modulation-doped GaAs v-groove quantum wires (QWRs) have been fabricated with
novel electrical contacts made to two-dimensional electron-gas (2DEG)
reservoirs. Here, we present longitudinal photocurrent (photoconductivity/PC)
spectroscopy measurements of a single QWR. We clearly observe conductance in
the ground-state one-dimensional subbands; in addition, a highly
temperature-dependent response is seen from other structures within the
v-groove. The latter phenomenon is attributed to the effects of structural
topography and localization on carrier relaxation. The results of
power-dependent PC measurements suggest that the QWR behaves as a series of
weakly interacting localized states, at low temperatures
Coherent current transport in wide ballistic Josephson junctions
We present an experimental and theoretical investigation of coherent current
transport in wide ballistic superconductor-two dimensional electron
gas-superconductor junctions. It is found experimentally that upon increasing
the junction length, the subharmonic gap structure in the current-voltage
characteristics is shifted to lower voltages, and the excess current at
voltages much larger than the superconducting gap decreases. Applying a theory
of coherent multiple Andreev reflection, we show that these observations can be
explained in terms of transport through Andreev resonances.Comment: 4 pages, 4 figure
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