46 research outputs found
Single Wall Carbon Nanotube Weak Links
We have reproducibly contacted gated single wall carbon nanotubes (SWCNT) to
superconducting leads based on niobium. The devices are identified to belong to
two transparency regimes: The Coulomb blockade and the Kondo regime. Clear
signature of the superconducting leads is observed in both regimes and in the
Kondo regime a narrow zero bias peak interpreted as a proximity induced
supercurrent persist in Coulomb blockade diamonds with Kondo resonances.Comment: Proceeding for International Symposium on Mesoscopic
Superconductivity and Spintronics 2006, NTT BRL, Atsugi, Japa
Multiple Andreev reflections in diffusive SNS structures
We report new measurements on sup-gap energy structure originating from
multiple Andreev reflections in mesoscopic SNS junctions. The junctions were
fabricated in a planar geometry with high transparency superconducting contacts
of Al deposited on highly diffusive and surface d-doped n++-GaAs. For samples
with a normal GaAs region of active length 0.3um the Josephson effect with a
maximal supercurrent Ic=3mA at T=237mK was observed. The sub-gap structure was
observed as a series of local minima in the differential resistance at dc bias
voltages V=2D/ne with n=1,2,4 i.e. only the even sub-gap positions. While at
V=2D/e (n=1) only one dip is observed, the n=2, and the n=4 sub-gap structures
each consists of two separate dips in the differential resistance. The mutual
spacing of these two dips is independent of temperature, and the mutual spacing
of the n=4 dips is half of the spacing of the n=2 dips. The voltage bias
positions of the sub-gap differential resistance minima coincide with the
maxima in the oscillation amplitude when a magnetic field is applied in an
interferometer configuration, where one of the superconducting electrodes has
been replaced by a flux sensitive open loop.Comment: 20 pages, 7 figure
Kondo physics in tunable semiconductor nanowire quantum dots
We have observed the Kondo effect in strongly coupled semiconducting nanowire
quantum dots. The devices are made from indium arsenide nanowires, grown by
molecular beam epitaxy, and contacted by titanium leads. The device
transparency can be tuned by changing the potential on a gate electrode, and
for increasing transparencies the effects dominating the transport changes from
Coulomb Blockade to Universal Conductance Fluctuations with Kondo physics
appearing in the intermediate region.Comment: 4 pages, 4 figure
Kondo-enhanced Andreev tunneling in InAs nanowire quantum dots
We report measurements of the nonlinear conductance of InAs nanowire quantum
dots coupled to superconducting leads. We observe a clear alternation between
odd and even occupation of the dot, with sub-gap-peaks at
markedly stronger(weaker) than the quasiparticle tunneling peaks at
for odd(even) occupation. We attribute the enhanced
-peak to an interplay between Kondo-correlations and Andreev tunneling
in dots with an odd number of spins, and substantiate this interpretation by a
poor man's scaling analysis
Observation of supercurrent enhancement in SNS junctions by non-equilibrium injection into supercurrent carrying bound Andreev states
We report for the first time enhancement of the supercurrent by means of
injection in a mesoscopic three terminal planar SNSNS device made of Al on
GaAs. When a current is injected from one of the superconducting Al electrodes
at an injection bias , the DC Josephson current between the
other two superconducting electrodes has a maximum, giving evidence for an
enhancement due to a non-equilibrium injection into bound Andreev states of the
underlying semiconductor. The effect persists to temperatures where the
equilibrium supercurrent has vanished.Comment: 7 pages + 3 figures. Resubmitted to Phys. Rev. Lett. Contents change