17 research outputs found
Coherent transport in extremely underdoped Nd1.2Ba1.8Cu3Oz nanostructures
Proximity-effect and resistance magneto-fluctuations measurements in
submicron Nd1.2Ba1.8Cu3Oz (NBCO) nano-loops are reported to investigate
coherent charge transport in the non-superconducting state. We find an
unexpected inhibition of cooper pair transport, and a destruction of the
induced superconductivity, by lowering the temperature from 6K to 250mK. This
effect is accompanied by a significant change in the conductance-voltage
characteristics and in the zero bias conductance response to the magnetic field
pointing to the activation of a strong pair breaking mechanism at lower
temperature. The data are discussed in the framework of mesoscopic effects
specific to superconducting nanostructures, proximity effect and high
temperature superconductivity.Comment: to appear on new journal of Physic
Quantum crossover in moderately damped epitaxial NbN/MgO/NbN junctions with low critical current density
High quality epitaxial NbN/MgO/NbN Josephson junctions have been realized
with MgO barriers up to a thickness of d=1 nm. The junction properties
coherently scale with the size of barrier, and low critical current densities
down to 3 A/cm have been achieved for larger barriers. In this limit,
junctions exhibit macroscopic quantum phenomena for temperatures lower than 90
mK. Measurements and junction parameters support the notion of a possible use
of these devices for multiphoton quantum experiments, taking advantage of the
fast non equilibrium electron-phonon relaxation times of NbN
Little-Parks effect in single YBaCuO sub-micron rings
The properties of single submicron high-temperature superconductor (HTS)
rings are investigated. The Little-Parks effect is observed and is accompanied
by an anomalous behavior of the magnetic dependence of the resistance, which we
ascribe to non-uniform vorticity (superfluid angular momentum) within the ring
arms. This effect is linked to the peculiar HTS-relationship between the values
of the coherence length and the London penetration depth.Comment: 14 pages, 3 figure
Thermal hopping and retrapping of a Brownian particle in the tilted periodic potential of a NbN/MgO/NbN Josephson junction
We report on the occurrence of multiple hopping and retrapping of a Brownian
particle in a tilted washboard potential. The escape dynamic has been studied
experimentally by measuring the switching current distributions as a function
of temperature in a moderately damped NbN/MgO/NbN Josephson junction. At low
temperatures the second moment of the distribution increases in agreement with
calculations based on Kramers thermal activation regime. After a turn-over
temperature T*, the shape of the distributions starts changing and width
decreases with temperature. We analyze the data through fit of the switching
probability and Monte Carlo simulations and we find a good agreement with a
model based on a multiple retrapping process
Terahertz Spectroscopy of Amorphous WSe2 and MoSe2 Thin Films
Time domain spectroscopy is used to determine the THz electromagnetic response of amorphous transition metal dichalcogenides WSe2 and MoSe2 in thin-film form. The dielectric function is obtained using a rigorous transmission model to account for the large etalon effect. The Drude–Smith model is applied to retrieve the dielectric function, and from there, the sample conductivity
A hybrid tunable THz metadevice using a high birefringence liquid crystal
We investigate a hybrid re-configurable three dimensional metamaterial based on liquid crystal as tuning element in order to build novel devices operating in the terahertz range. The proposed metadevice is an array of meta-atoms consisting of split ring resonators having suspended conducting cantilevers in the gap region. Adding a “third dimension” to a standard planar device plays a dual role: (i) enhance the tunability of the overall structure, exploiting the birefringence of the liquid crystal at its best, and (ii) improve the field confinement and therefore the ability of the metadevice to efficiently steer the THz signal. We describe the design, electromagnetic simulation, fabrication and experimental characterization of this new class of tunable metamaterials under an externally applied small voltage. By infiltrating tiny quantities of a nematic liquid crystal in the structure, we induce a frequency shift in the resonant response of the order of 7–8% in terms of bandwidth and about two orders of magnitude change in the signal absorption. We discuss how such a hybrid structure can be exploited for the development of a THz spatial light modulator
Terahertz Spectroscopy of Amorphous WSe2 and MoSe2 Thin Films
Time domain spectroscopy is used to determine the THz electromagnetic response of amorphous transition metal dichalcogenides WSe2 and MoSe2 in thin-film form. The dielectric function is obtained using a rigorous transmission model to account for the large etalon effect. The Drude–Smith model is applied to retrieve the dielectric function, and from there, the sample conductivity