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ABSTRACT: We have measured the temperature dependence of the microwave surface impedance Z_s = R_s + i\Omega\mu_0 of a MgB2 film at a frequency \Omega /2\Pi of 18 GHz employing a dielectric resonator technique. We found that the temperature dependence of the magnetic field penetration depth \Lamda can be fitted by \Lamda(T)= \Lamda(0) [1-(T/Tc)^2] ^(-1/2) with \Lamda(0)=(260 +/- 20)nm. The absolute value of \Lamda(0) was confirmed by direct measurements employing submillimeter wave transmission spectroscopy at 430 GHz. The analysis of the \Lamda(T) data below Tc/2 revealed significant deviations from the quadratic temperature dependence. In contrast, we found that an exponential temperature dependence fits the experimental data within the statistical measurement error for temperature changes of \Lamda of +/- 0.4 nm. This observation indicates thermal excitation of quasiparticles over a finite energy gap of (3.3 +/- 0.3) meV corresponding to \Delta /kTc = 1.2 +/- 0.1. Our results strongly supports a multipgap or a strongly anisotropic gap and the absence of nodes in the gap function.
08/2001;
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ABSTRACT: Dielectric resonator filters for C-band and Ku-band were designed
and built. The C-band filter was based on the HEM(11<sup>δ</sup>)
dual-mode of hemispherical resonators machined from BaMgTaO ceramics,
which has a dielectric constant of around 24. The Ku-band filter was
based on the HEM(11<sup>δ</sup>) dual-mode of cylindrical
resonators machined from sapphire single crystals. For both filters with
cavity made from copper, unloaded quality factors of 30,000 and more
than 60,000 were registered at room temperature and 77 K, respectively.
For a four-pole quasi-elliptic filter with center frequency of around
3.72 GHz and bandwidth of 36 MHz, the measured insertion loss was 0.17
dB at room temperature and 0.08 dB at 77 K. For a four-pole
quasi-elliptic filter with center frequency of 10.76 GHz and bandwidth
of 24 MHz, the measured insertion loss was 0.9 dB at room temperature.
We also estimated the unloaded quality factor of the C-band filter when
the top copper endplate was replaced by a YBa<sub>2</sub>Cu<sub>3</sub>O
<sub>7</sub> superconducting film. In this case the unloaded quality
factor was 100,000 at 77 K
IEEE Transactions on Appiled Superconductivity 04/2001; · 1.04 Impact Factor
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ABSTRACT: Recent progress in manufacturing dielectric ceramics and single crystals with high dielectric constant and low microwave losses has turned out to be a challenge for the development of novel devices for satellite communication. From this development device performance is expected to benefit for possible device operation temperatures ranging from cryogenic temperatures around 50-150 K (achievable with one-stage closed cycle refrigerators) over temperatures from 150 to 200 K (in principal achievable with radiation cooling) towards room temperature, if novel dielectric resonator structures with lower loss contribution of the metallic housing became available.
Superconductor Science and Technology 05/2000; 13(5):527. · 2.66 Impact Factor
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ABSTRACT: This paper demonstrates a design of a planar multi-turn flux
transformer integrated with a superconducting labyrinth resonator
serving as the planar tank circuit for a radio frequency (rf)
superconducting quantum interference device (SQUID) magnetometer. All
structures were patterned from 200 nm-thick epitaxial YBa<sub>2</sub>Cu
<sub>3</sub>O<sub>7</sub> (YBCO) films grown on 10×10 mm<sup>2
</sup> LaAlO<sub>3</sub> substrates. A double-hole washer SQUID had one
hole coupled to the input coil of the labyrinth resonator and the other
hole coupled to the input coil of the multi-turn flux transformer using
a flip-chip configuration to form a magnetometer. This resonator has a
good high-frequency coupling to the double-hole rf SQUID, thus securing
its optimum operation. For the voltage-to-flux (transfer function)
coefficient, a value of 300-500 μV/Φ<sub>0</sub> was obtained. A
SQUID magnetometer with an inductance of 210 pH exhibited white flux
noise of 11.5 μΦ<sub>0</sub>/√Hz at 77 K. This corresponded
to a white magnetic field noise of 11.5 fT/√Hz
IEEE Transactions on Appiled Superconductivity 07/1999; · 1.04 Impact Factor
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ABSTRACT: The coupling coefficient (k<sup>2</sup>) between the
superconducting coplanar resonator and the flip chip coupled washer
radio frequency SQUID was calculated using computer simulation. The
coplanar resonator is formed by two coplanar lines surrounding a flux
concentrator with each line having a slit. For a 3 mm×3 mm washer
SQUID with a 100 μm×100 μm loop coupled to a coplanar
resonator with the slits on opposite sides, we estimated
k<sup>2</sup>=7.1×10<sup>-3</sup>. However, if the same SQUID is
coupled to a coplanar resonator with parallel slits and with a short
circuit at the 90° position with respect to the opening slit,
k<sup>2</sup> of only 0.5×10<sup>-3</sup> is obtained, which
indicates that the k<sup>2</sup> is strongly dependent on the resonator
layout. The simulation also shows that k<sup>2</sup> is dependent on the
SQUID washer size and the separation distance between the washer SQUID
and the coplanar resonator
IEEE Transactions on Appiled Superconductivity 07/1999; · 1.04 Impact Factor
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IEEE Transactions on Appiled Superconductivity 01/1999; 9(2):3813-3816. · 1.04 Impact Factor
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ABSTRACT: This work showed experimentally how the planar multiturn input coil of a flux transformer could be integrated with a coplanar resonator while still permitting one to couple radio frequency (rf) signals to an rf SQUID. A new layout of a multiturn flux transformer with one pickup loop and two input coils, one single turn and one multiturn, has been fabricated on (001) substrates and evaluated. A planar double-hole washer SQUID was inductively coupled to the two separate input coils via a flip chip configuration. With this layout the best magnetometer showed magnetic field white noise of at 77 K in a magnetically shielded surrounding.
Superconductor Science and Technology 12/1998; 11(7):692. · 2.66 Impact Factor
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ABSTRACT: We have simulated the superconducting coplanar resonators of different designs that we have fabricated and tested as the tank circuit of radio frequency superconducting quantum interference devices. The coplanar resonator is formed by two microstrip lines surrounding a flux concentrator with each line having a slit. The simulated resonant frequencies agreed well with the experimental values, where frequencies decreased with an increasing mutual angular position between the two microstrip slits, and with a short circuit between the two microstrip lines. The simulation also showed that the loss in the system is mainly contributed by the dielectric loss of the substrate materials. © 1998 American Institute of Physics.
Applied Physics Letters 10/1998; 73(16):2357-2359. · 3.84 Impact Factor
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ABSTRACT: We propose a design for planar multi-turn flux transformer for radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. This transformer is integrated with a coplanar resonator, e.g., on a 1 cm2 LaAlO3 substrate. Its pickup loop is connected with two input coils, separate for dc (low-frequency) and rf currents. A double-hole washer SQUID is coupled to these coils in a flip-chip configuration to form a magnetometer. The separation of rf and dc current paths in the transformer made it possible to demonstrate the rf SQUID magnetometer operation. © 1998 American Institute of Physics.
Applied Physics Letters 04/1998; 72(16):2029-2031. · 3.84 Impact Factor
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Applied Superconductivity 1997, Vols 1 and 2 - Vol 1: Small Scale and Electronic Applications; Vol 2: Large Scale and Power Applications. 01/1997;
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ABSTRACT: We have developed a novel coplanar resonator serving as a tank circuit for rf washer supercenductry quantum interference device (SQUID)s. Two coplanar lines surround flux concentrator washers. The SQUID, 2.5 or 3.5 mm in diameter, is coupled to the concentrator in the flip-chip configuration. In these layouts, the adjustable resonant frequency is up to the GHz-range. With SQUID loops of 10×500 μm2 (SQUID inductance Ls=260 pH), we measured at 77 K white flux noise levels Sφ1/2 of 8.5 μφ0/√Hz. This corresponded to an energy resolution ϵ of 850 h and a field resolution of about 16 fT/√Hz for a concentrator diameter of 13.4 mm.
Applied Superconductivity.
