23 research outputs found
Proximity effect in planar Superconductor/Semiconductor junction
We have measured the very low temperature (down to 30 mK) subgap resistance
of Titanium Nitride (Superconductor, Tc = 4.6 K)/highly doped Silicon
(Semiconductor) SIN junction (the insulating layer stands for the Schottky
barrier). As the temperature is lowered, the resistance increases as expected
in SIN junction. Around 300 mK, the resistance shows a maximum and decreases at
lower temperature. This observed behavior is due to coherent backscattering
towards the interface by disorder in Silicon ("Reflectionless tunneling"). This
effect is also observed in the voltage dependence of the resistance (Zero Bias
Anomaly) at low temperature (T<300 mK). The overall resistance behavior (in
both its temperature and voltage dependence) is compared to existing theories
and values for the depairing rate, the barrier resistance and the effective
carrier temperature are extracted.Comment: Submitted to LT22, Helsinki - August 1999, phbauth.cls include
Sub-Gap Structure in the Conductance of a Three-Terminal Josephson Junction
Three-terminal superconductor (S) - normal metal (N) - superconductor (S)
Josephson junctions are investigated. In a geometry where a T-shape normal
metal is connected to three superconducting reservoirs, new sub-gap structures
appear in the differential resistance for specific combinations of the
superconductor chemical potentials. Those correspond to a correlated motion of
Cooper pairs within the device that persist well above the Thouless energy and
is consistent with the prediction of quartets formed by two entangled Cooper
pairs. A simplified nonequilibrium Keldysh Green's function calculation is
presented that supports this interpretation.Comment: To appear in Physical Review
Half-integer Shapiro steps at the 0-pi crossover of a ferromagnetic Josephson junction
We investigate the current-phase relation of S/F/S junctions near the
crossover between the 0 and the pi ground states. We use Nb/CuNi/Nb junctions
where this crossover is driven both by thickness and temperature. For a certain
thickness a non-zero minimum of critical current is observed at the crossover
temperature. We analyze this residual supercurrent by applying a high frequency
excitation and observe the formation of half-integer Shapiro steps. We
attribute these fractional steps to a doubling of the Josephson frequency due
to a sin(2*phi) current-phase relation. This phase dependence is explained by
the splitting of the energy levels in the ferromagnetic exchange field.Comment: 4 pages, 5 figures, accepted for publication in Phys. Rev. Let
A gate-tunable graphene Josephson parametric amplifier
With a large portfolio of elemental quantum components, superconducting
quantum circuits have contributed to dramatic advances in microwave quantum
optics. Of these elements, quantum-limited parametric amplifiers have proven to
be essential for low noise readout of quantum systems whose energy range is
intrinsically low (tens of eV ). They are also used to generate non
classical states of light that can be a resource for quantum enhanced
detection. Superconducting parametric amplifiers, like quantum bits, typically
utilize a Josephson junction as a source of magnetically tunable and
dissipation-free nonlinearity. In recent years, efforts have been made to
introduce semiconductor weak links as electrically tunable nonlinear elements,
with demonstrations of microwave resonators and quantum bits using
semiconductor nanowires, a two dimensional electron gas, carbon nanotubes and
graphene. However, given the challenge of balancing nonlinearity, dissipation,
participation, and energy scale, parametric amplifiers have not yet been
implemented with a semiconductor weak link. Here we demonstrate a parametric
amplifier leveraging a graphene Josephson junction and show that its working
frequency is widely tunable with a gate voltage. We report gain exceeding 20 dB
and noise performance close to the standard quantum limit. Our results complete
the toolset for electrically tunable superconducting quantum circuits and offer
new opportunities for the development of quantum technologies such as quantum
computing, quantum sensing and fundamental science
Magnetic-spin-echo response to a moving vortex lattice in a type-II superconductor
International audienc
HCNH+ abundance in cold dense clouds based on the first hyperfine resolved rate coefficients
International audienceThe protonated form of hydrogen cyanide, HCNH+, holds significant importance in astrochemistry, serving as an intermediate species in ion-neutral reactions occurring in the cold molecular clouds. Although it plays a crucial role in the chemistry of HCN and HNC, the excitation rate coe fficients of this molecular cation by the dominant interstellar colliders have not been thoroughly investigated, leading to limitations in the radiative transfer models used to derive its abundance. In this work, we present the first hyperfine-resolved excitation rate coe fficients for HCNH+ induced by collisions with both He and H-2 at low temperatures, addressing a crucial requirement for precise modeling of HCNH+ abundance in typical cold dense molecular clouds. Using non-local thermodynamic equilibrium (non-LTE) radiative transfer calculations, we reproduced the 1 -> 0 and 2 -> 1 observational spectra of HCNH+ fairly well and derived updated molecular column densities. For the TMC-1 molecular cloud, the new HCNH+ abundance is twice as large as suggested by previous LTE modeling, whereas the column density of this molecular cation is improved only by 10% in the case of the L483 proto-star. The factor of two in the case of TMC-1 most likely arises from an error in the early analysis of observational spectra rather than an effect of the LTE assumption, given that the HCNH+ lines are predominantly thermalized at densities higher than 2 x 10(4) cm(-3). For multiline studies of clouds of moderate densities, we strongly recommend using the collisional rate coe fficients reported in this work
Proximity-induced superconductivity in all-silicon superconductor /normal-metal junctions
International audienc
Influence of substrate-induced thermal stress on the superconducting properties of V 3 Si thin films
International audienc