182 research outputs found
Inelastic relaxation and noise temperature in S/N/S junctions
We studied electronic relaxation in long diffusive superconductor / normal
metal / superconductor (S/N/S) junctions by means of current noise and
transport measurements down to very low temperature (100mK). Samples with
normal metal lengths of 4, 10 and 60 micrometer have been investigated. In all
samples the shot noise increases very rapidly with the voltage. This is
interpreted in terms of enhanced heating of the electron gas confined between
the two S/N interfaces. Experimental results are analyzed quantitatively taking
into account electron-phonon interaction and heat transfer through the S/N
interfaces. Transport measurements reveal that in all samples the two S/N
interfaces are connected incoherently, as shown by the reentrance of the
resistance at low temperature. The complementarity of noise and transport
measurements allows us to show that the energy dependence of the reentrance at
low voltage is essentially due to the increasing effective temperature of the
quasiparticles in the normal metal.Comment: 5 pages, 4 figures, to be published in EPJ
Conductance statistics in small insulating GaAs:Si wires at low temperature. II. Experimental study
We have observed reproducible conductance fluctuations at low temperature in
a small GaAs:Si wire driven across the Anderson transition by the application
of a gate voltage. We analyse quantitatively the log-normal conductance
statistics in terms of truncated quantum fluctuations. Quantum fluctuations due
to small changes of the electron energy (controlled by the gate voltage) cannot
develop fully due to identified geometrical fluctuations of the resistor
network describing the hopping through the sample.
The evolution of the fluctuations versus electron energy and magnetic field
shows that the fluctuations are non-ergodic, except in the critical insulating
region of the Anderson transition, where the localization length is larger than
the distance between Si impurities.
The mean magnetoconductance is in good accordance with simulations based on
the Forward-Directed-Paths analysis, i.e. it saturates to as decreases over orders of
magnitude in the strongly localized regime.Comment: Email contact: [email protected]
Proximity effect in planar TiN-Silicon junctions
We measured the low temperature subgap resistance of titanium nitride
(superconductor, Tc=4.6K)/highly doped silicon (degenerated semiconductor) SIN
junctions, where I stands for the Schottky barrier. At low energies, the subgap
conductance is enhanced due to coherent backscattering of the electrons towards
the interface by disorder in the silicon (''reflectionless tunneling''). This
Zero Bias Anomaly (ZBA) is destroyed by the temperature or the magnetic field
above 250mK or 0.04T respectively. The overall differential resistance behavior
(vs temperature and voltage) is compared to existing theories and values for
the depairing rate and the barrier transmittance are extracted. Such an
analysis leads us to introduce an effective temperature for the electrons and
to discuss heat dissipation through the SIN interface.Comment: 23 pages, 6 figures, added references and minor corrections. Accepted
to Journal of Low Temperature Physic
Mesoscopic transition in the shot noise of diffusive S/N/S junctions
We experimentally investigated the current noise in diffusive
Superconductor/Normal metal/Superconductor junctions with lengths between the
superconducting coherence length xi_Delta and the phase coherence length L_Phi
of the normal metal (xi_Delta < L < L_Phi). We measured the shot noise over a
large range of energy covering both the regimes of coherent and incoherent
multiple Andreev reflections. The transition between these two regimes occurs
at the Thouless energy where a pronounced minimum in the current noise density
is observed. Above the Thouless energy, in the regime of incoherent multiple
Andreev reflections, the noise is strongly enhanced compared to a normal
junction and grows linearly with the bias voltage. Semi-classical theory
describes the experimental results accurately, when taking into account the
voltage dependence of the resistance which reflects the proximity effect. Below
the Thouless energy, the shot noise diverges with decreasing voltage which may
indicate the coherent transfer of multiple charges.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. B, Rapid
Communicatio
A simple and controlled single electron transistor based on doping modulation in silicon nanowires
A simple and highly reproducible single electron transistor (SET) has been
fabricated using gated silicon nanowires. The structure is a
metal-oxide-semiconductor field-effect transistor made on silicon-on-insulator
thin films. The channel of the transistor is the Coulomb island at low
temperature. Two silicon nitride spacers deposited on each side of the gate
create a modulation of doping along the nanowire that creates tunnel barriers.
Such barriers are fixed and controlled, like in metallic SETs. The period of
the Coulomb oscillations is set by the gate capacitance of the transistor and
therefore controlled by lithography. The source and drain capacitances have
also been characterized. This design could be used to build more complex SET
devices.Comment: to be published in Applied Physics Letter
Doubled Full Shot Noise in Quantum Coherent Superconductor - Semiconductor Junctions
We performed low temperature shot noise measurements in Superconductor (TiN)
- strongly disordered normal metal (heavily doped Si) weakly transparent
junctions. We show that the conductance has a maximum due to coherent multiple
reflections at low energy and that shot noise is then twice the Poisson noise
(S=4eI). The shot noise changes to the normal value (S=2eI) due to a large
quasiparticle contribution.Comment: published in Physical Review Letter
Design and cryogenic operation of a hybrid quantum-CMOS circuit
Silicon-On-Insulator nanowire transistors of very small dimensions exhibit
quantum effects like Coulomb blockade or single-dopant transport at low
temperature. The same process also yields excellent field-effect transistors
(FETs) for larger dimensions, allowing to design integrated circuits. Using the
same process, we have co-integrated a FET-based ring oscillator circuit
operating at cryogenic temperature which generates a radio-frequency (RF)
signal on the gate of a nanoscale device showing Coulomb oscillations. We
observe rectification of the RF signal, in good agreement with modeling
Reconfigurable quadruple quantum dots in a silicon nanowire transistor
We present a novel reconfigurable metal-oxide-semiconductor multi-gate
transistor that can host a quadruple quantum dot in silicon. The device consist
of an industrial quadruple-gate silicon nanowire field-effect transistor.
Exploiting the corner effect, we study the versatility of the structure in the
single quantum dot and the serial double quantum dot regimes and extract the
relevant capacitance parameters. We address the fabrication variability of the
quadruple-gate approach which, paired with improved silicon fabrication
techniques, makes the corner state quantum dot approach a promising candidate
for a scalable quantum information architecture
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