171 research outputs found
Single Superconducting Split-Ring Resonator Electrodynamics
We investigate the microwave electrodynamic properties of a single
superconducting thin film split-ring resonator (SRR). The experiments were
performed in an all-Nb waveguide, with Nb wires and Nb SRRs. Transmission data
showed a high-Q stopband for a single Nb SRR ( at 4.2 K)
below , and no such feature for a Cu SRR, or closed Nb loops, of similar
dimensions. Adding SRRs increased the bandwidth, but decreased the insertion
loss of the features. Placing the Nb SRR into an array of wires produced a
single, elementary negative-index passband ( at 4.2 K).
Changes in the features due to the superconducting kinetic inductance were
observed. Models for the SRR permeability, and the wire dielectric response,
were used to fit the data.Comment: 4 pages, 3 figures, RevTex, submitted to Applied Physics Letters.
Updated version includes mention of bianisotropy, better looking figures, and
different temperature dat
High Gradients In Linear Collider Superconducting Accelerator cavities By high Pulsed Power To Suppress Field Emission
Strong Electron-Phonon Coupling in Superconducting MgB: A Specific Heat Study
We report on measurements of the specific heat of the recently discovered
superconductor MgB in the temperature range between 3 and 220 K. Based on a
modified Debye-Einstein model, we have achieved a rather accurate account of
the lattice contribution to the specific heat, which allows us to separate the
electronic contribution from the total measured specific heat. From our result
for the electronic specific heat, we estimate the electron-phonon coupling
constant to be of the order of 2, significantly enhanced compared to
common weak-coupling values . Our data also indicate that the
electronic specific heat in the superconducting state of MgB can be
accounted for by a conventional, s-wave type BCS-model.Comment: 4 pages, 4 figure
Tunable coaxial cavity resonator for linear and nonlinear microwave characterization of superconducting wires
We discuss experimental results obtained using a tunable cylindrical coaxial
cavity constituted by an outer Cu cylinder and an inner Pb-BSCCO wire. We have
used this device for investigating the microwave response of the
superconducting wire, both in the linear and nonlinear regimes. In particular,
by tuning the different modes of the cavity to make them resonant at exactly
harmonic frequencies, we have detected the power emitted by the superconducting
inner wire at the second- and third-harmonic frequency of the driving field.
The results obtained in the nonlinear regime, whether for the microwave surface
impedance or the harmonic emission, are qualitatively accounted for considering
intergrain fluxon dynamics. The use of this kind of device can be of strong
interest to investigate and characterise wires of large dimensions to be used
for implementing superconducting-based microwave devices.Comment: 14 pages, 6 embedded figures, accepted for publication in Supercond.
Sci. Techno
Superconducting Microwave Cavity Made of Bulk MgB2
We report the successful manufacture and characterization of a microwave
resonant cylindrical cavity made of bulk MgB2 superconductor (Tc = 38.5 K),
which has been produced by the Reactive Liquid Mg Infiltration technique. The
quality factor of the cavity for the TE011 mode, resonating at 9.79 GHz, has
been measured as a function of the temperature. At T = 4.2 K, the unloaded
quality factor is 2.2x10^5; it remains of the order of 10^5 up to T ~ 30 K. We
discuss the potential performance improvements of microwave cavities built from
bulk MgB2 materials produced by reactive liquid Mg infiltration.Comment: 7 pages, 2 embedded figures, accepted for publication in Supercond.
Sci. Techno
Observation of a Chiral State in a Microwave Cavity
A microwave experiment has been realized to measure the phase difference of
the oscillating electric field at two points inside the cavity. The technique
has been applied to a dissipative resonator which exhibits a singularity --
called exceptional point -- in its eigenvalue and eigenvector spectrum. At the
singularity, two modes coalesce with a phase difference of We
conclude that the state excited at the singularity has a definitiv chirality.Comment: RevTex 4, 5 figure
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