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Signal Amplification in NbN Superconducting Resonators via Stochastic Resonance  [PDF]
Baleegh Abdo,Eran Arbel-Segev,Oleg Shtempluck,Eyal Buks
Physics , 2006, DOI: 10.1016/j.physleta.2007.05.103
Abstract: We exploit nonlinearity in NbN superconducting stripline resonators, which is originated by local thermal instability, for studying stochastic resonance. As the resonators are driven into instability, small amplitude modulated (AM) microwave signals are amplified with the aid of injected white noise. The dependence of the signal amplification on the modulation amplitude and the modulation frequency is examined and compared with theory.
Intermodulation Gain in Nonlinear NbN Superconducting Microwave Resonators  [PDF]
B. Abdo,E. Segev,O. Shtempluck,E. Buks
Physics , 2005, DOI: 10.1063/1.2164925
Abstract: We report the measurement of intermodulation gain in NbN superconducting stripline resonators. In the intermodulation measurements we inject two unequal tones into the oscillator, the pump and signal, both lying within the resonance band. At the onset of instability of the reflected pump we obtain a simultaneous gain of both the idler and the reflected signal. The measured gain in both cases can be as high as 15 dB, whereas to the best of our knowledge intermodulation gain greater than unity in superconducting resonators has not been reported before in the scientific literature.
Thermal Instability and Self-Sustained Modulation in Superconducting NbN Stripline Resonators  [PDF]
Eran Arbel-Segev,Baleegh Abdo,Oleg Shtempluck,Eyal Buks
Physics , 2006,
Abstract: We study theoretically and experimentally the response of a microwave superconducting stripline resonator, integrated with a microbridge, to a monochromatic injected signal. We find that there is a certain range of driving parameters, in which a novel nonlinear phenomenon immerges, and self-sustained modulation of the reflected power off the resonator is generated by the resonator. A theoretical model which attributes the self modulation to a thermal instability yields a good agreement with the experimental results.
Observation of Bifurcations and Hysteresis in Nonlinear NbN Superconducting Microwave Resonators  [PDF]
Baleegh Abdo,Eran Segev,Oleg Shtempluck,Eyal Buks
Physics , 2005, DOI: 10.1109/TASC.2006.881823
Abstract: In this paper we report some extraordinary nonlinear dynamics measured in the resonance curve of NbN superconducting stripline microwave resonators. Among the nonlinearities observed: aburpt bifurcations in the resonance response at relatively low input powers, asymmetric resonances, multiple jumps within the resonance band, resonance frequency drift, frequency hysteresis, hysteresis loops changing direction and critical coupling phenomenon. Weak links in the NbN grain structure are hypothesized as the source of the nonlinearities.
Niobium stripline resonators for microwave studies on superconductors  [PDF]
Markus Thiemann,Daniel Bothner,Dieter Koelle,Reinhold Kleiner,Martin Dressel,Marc Scheffler
Physics , 2014, DOI: 10.1088/1742-6596/568/2/022043
Abstract: Microwave spectroscopy is a powerful experimental tool to reveal information on the intrinsic properties of superconductors. Superconducting stripline resonators, where the material under study constitutes one of the ground planes, offer a high sensitivity to investigate superconducting bulk samples. In order to improve this measurement technique, we have studied stripline resonators made of niobium, and we compare the results to lead stripline resonators. With this technique we are able to determine the temperature dependence of the complex conductivity of niobium and the energy gap $\Delta(0)=2.1$ meV. Finally we show measurements at the superconducting transition of a tantalum bulk sample using niobium stripline resonators.
Stochastic Resonance with a Single Metastable State  [PDF]
Eran Segev,Baleegh Abdo,Oleg Shtempluck,Eyal Buks
Physics , 2007, DOI: 10.1103/PhysRevB.77.012501
Abstract: We study thermal instability in NbN superconducting stripline resonators. The system exhibits extreme nonlinearity near a bifurcation, which separates a monostable zone and an astable one. The lifetime of the metastable state, which is locally stable in the monostable zone, is measure near the bifurcation and the results are compared with a theory. Near bifurcation, where the lifetime becomes relatively short, the system exhibits strong amplification of a weak input modulation signal. We find that the frequency bandwidth of this amplification mechanism is limited by the rate of thermal relaxation. When the frequency of the input modulation signal becomes comparable or larger than this rate the response of the system exhibits sub-harmonics of various orders.
Surface-resistance measurements using superconducting stripline resonators  [PDF]
Daniel Hafner,Martin Dressel,Marc Scheffler
Physics , 2013, DOI: 10.1063/1.4856475
Abstract: We present a method to measure the absolute surface resistance of conductive samples at a set of GHz frequencies with superconducting lead stripline resonators at temperatures 1- 6K. The stripline structure can easily be applied for bulk samples and allows direct calculation of the surface resistance without the requirement of additional calibration measurements or sample reference points. We further describe a correction method to reduce experimental background on high-Q resonance modes by exploiting TEM-properties of the external cabling. We then show applications of this method to the reference materials gold, tantalum, and tin, which include the anomalous skin effect and conventional superconductivity. Furthermore, we extract the complex optical conductivity for an all-lead stripline resonator to find a coherence peak and the superconducting gap of lead.
Nonlinear Coupling in Nb/NbN Superconducting Microwave Resonators  [PDF]
Baleegh Abdo,Eran Segev,Oleg Shtempluck,Eyal Buks
Physics , 2005,
Abstract: In this experimental study we show that the coupling between Nb/NbN superconducting microwave resonators and their feedline can be made amplitude dependent. We employ this mechanism to tune the resonators into critical coupling condition, a preferable mode of operation for a wide range of applications. Moreover we examine the dependence of critical coupling state on other parameters such as temperature and magnetic field. Possible novel applications based on such nonlinear coupling are briefly discussed.
Prospects of employing superconducting stripline resonators for studying the dynamical Casimir effect experimentally  [PDF]
Eran Arbel-Segev,Baleegh Abdo,Oleg Shtempluck,Eyal Buks,Bernard Yurke
Physics , 2006,
Abstract: We discuss the prospects of employing an NbN superconducting microwave stripline resonator for studying the dynamical Casimir effect experimentally. Preliminary experimental results, in which optical illumination is employed for modulating the resonance frequencies of the resonator, show that such a system is highly promising for this purpose. Moreover, we discuss the undesirable effect of heating which results from the optical illumination, and show that degradation in noise properties can be minimized by employing an appropriate design.
Unexpected Nonlinear Dynamics in NbN Superconducting Microwave Resonators  [PDF]
Baleegh Abdo,Eran Segev,Oleg Shtempluck,Eyal Buks
Physics , 2005, DOI: 10.1103/PhysRevB.73.134513
Abstract: In this work we characterize the unusual nonlinear dynamics of the resonance response, exhibited by our NbN superconducting microwave resonators, using different operating conditions. The nonlinear dynamics, occurring at relatively low input powers (2-4 orders of magnitude lower than Nb), and which include among others, bifurcations in the resonance curve, hysteresis loops and resonance frequency shift, are measured herein using varying temperature, applied magnetic field, white noise and rapid frequency sweeps. Based on these measurement results, we consider a hypothesis according to which Josephson junctions forming weak links at the boundaries of the NbN grains are responsible for the observed behavior, and we show that most of the experimental results are qualitatively consistent with such hypothesis.
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