82 research outputs found
Coulomb blockade and Bloch oscillations in superconducting Ti nanowires
Quantum fluctuations in quasi-one-dimensional superconducting channels
leading to spontaneous changes of the phase of the order parameter by ,
alternatively called quantum phase slips (QPS), manifest themselves as the
finite resistance well below the critical temperature of thin superconducting
nanowires and the suppression of persistent currents in tiny superconducting
nanorings. Here we report the experimental evidence that in a current-biased
superconducting nanowire the same QPS process is responsible for the insulating
state -- the Coulomb blockade. When exposed to RF radiation, the internal Bloch
oscillations can be synchronized with the external RF drive leading to
formation of quantized current steps on the I-V characteristic. The effects
originate from the fundamental quantum duality of a Josephson junction and a
superconducting nanowire governed by QPS -- the QPS junction (QPSJ).Comment: 5 pages, 4 figure
Normal metal - insulator - superconductor interferometer
Hybrid normal metal - insulator - superconductor microstructures suitable for
studying an interference of electrons were fabricated. The structures consist
of a superconducting loop connected to a normal metal electrode through a
tunnel barrier . An optical interferometer with a beam splitter can be
considered as a classical analogue for this system. All measurements were
performed at temperatures well below 1 K. The interference can be observed as
periodic oscillations of the tunnel current (voltage) through the junction at
fixed bias voltage (current) as a function of a perpendicular magnetic field.
The magnitude of the oscillations depends on the bias point. It reaches a
maximum at energy which is close to the superconducting gap and decreases
with an increase of temperature. Surprisingly, the period of the oscillations
in units of magnetic flux is equal neither to nor to
, but significantly exceeds these values for larger loop circumferences.
The origin of the phenomena is not clear.Comment: 11 pages and 8 figure
The quantum phase slip phenomenon in superconducting nanowires with high-impedance environment
Quantum phase slip (QPS) is the particular manifestation of quantum
fluctuations of the order parameter of a current-biased quasi-1D
superconductor. The QPS event(s) can be considered a dynamic equivalent of
tunneling through conventional Josephson junction containing static in space
and time weak link(s). At low temperatures T<<Tc the QPS effect leads to finite
resistivity of narrow superconducting channels and suppresses persistent
currents in tiny nanorings. Here we demonstrate that the quantum tunneling of
phase may result in Coulomb blockade: superconducting nanowire, imbedded in
high-Ohmic environment, below a certain bias voltage behaves as an insulator.Comment: 3 pages, 3 figure
Microscopic model for multiple flux transitions in mesoscopic superconducting loops
A microscopic model is constructed which is able to describe multiple
magnetic flux transitions as observed in recent ultra-low temperature tunnel
experiments on an aluminum superconducting ring with normal metal - insulator -
superconductor junctions [Phys. Rev. B \textbf{70}, 064514 (2004)]. The unusual
multiple flux quantum transitions are explained by the formation of metastable
states with large vorticity. Essential in our description is the modification
of the pairing potential and the superconducting density of states by a
sub-critical value of the persistent current which modulates the measured
tunnel current. We also speculate on the importance of the injected
non-equilibrium quasiparticles on the stability of these metastable states.Comment: 6 pages, 3 figure
Quantum phase slip phenomenon in superconducting nanowires with low-Ohmic environment
In a number of recent experiments it has been demonstrated that in
ultra-narrow superconducting channels quantum fluctuations of the order
parameter, alternatively called quantum phase slips, are responsible for the
finite resistance well below the critical temperature. The acceptable agreement
between those experiments and the models describing quantum fluctuations in
quasi-one-dimensional superconductors has been established. However the very
concept of the phase slip is justified when these fluctuations are the
relatively rare events, meaning that the effective resistance of the system
should be much smaller than the normal state equivalent. In this paper we study
the limit of the strong quantum fluctuations where the existing models are not
applicable. In particular case of ultra-thin titanium nanowires it is
demonstrated that below the expected critical temperature the resistance does
not demonstrate any trend towards the conventional for a superconductor
zero-resistivity state even at negligibly small measuring currents. Application
of a small magnetic field leads to an unusual negative magnetoresistance, which
becomes more pronounced at lower temperatures. The origin of the negative
magnetoresistance effect is not clear
Spatially-resolved probing of a non-equilibrium superconductor
Spatially resolved relaxation of non-equilibrium quasiparticles in a
superconductor at ultra-low temperatures was experimentally studied. It was
found that the quasiparticle injection through a tunnel junction results in
modification of the shape of I-V characteristic of a remote `detector'
junction. The effect depends on temperature, injection current and proximity to
the injector. The phenomena can be understood in terms of creation of
quasiparticle charge and energy disequilibrium characterized by two different
length scales m and
m. The findings are in good agreement with existing phenomenological
models, while more elaborated microscopic theory is mandatory for detailed
quantitative comparison with experiment. The results are of fundamental
importance for understanding electron transport phenomena in various
nanoelectronic circuits.Comment: 7 pages, 5 figure
On Hamiltonian structure of the spin Ruijsenaars-Schneider model
The Hamiltonian structure of spin generalization of the rational
Ruijsenaars-Schneider model is found by using the Hamiltonian reduction
technique. It is shown that the model possesses the current algebra symmetry.
The possibility of generalizing the found Poisson structure to the
trigonometric case is discussed and degeneration to the Euler-Calogero-Moser
system is examined.Comment: latex, 16 pages, references are adde
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