3,874 research outputs found
SlowâWave Structures Utilizing Superconducting ThinâFilm Transmission Lines
Slowâwave propagation of electromagnetic waves in transmission lines formed of thinâfilm superconductors has been studied theoretically and experimentally. Previous theoretical analyses have been extended to include nonlocal theories. Strong dependence of phase velocity is found on film thickness and interfilm spacing when these become less than a few penetration depths. Velocity is also modified by coherence length, mean free path, nature of reflection of electrons at the film surfaces, and by temperature and magnetic field. Experimental measurements were made to verify the dependence on thickness, spacing, and temperature by means of a resonance technique. Agreement with theory was excellent in the case of temperature. Data taken for varying thickness and spacing verified the general trend of theoretical predictions. They indicate a nonlocal behavior with some specular reflection, but scatter of the data taken for different films prevents precise comparison of theory and experiment. Estimates of bulk penetration depths were made for indium, λ_In = 648±130 Ă
. For tantalum a rough estimate could be made of λTa = 580 Ă
. Data were consistent with the estimate of coherence length for indium of Ο_0 â 3000 Ă
. Velocity was found to be independent of frequency in the range 50â500 MHz, while losses increased as the square. Pulse measurements indicated that delays of several microseconds and storage of several thousand pulses on a single line are feasible
Broadband method for precise microwave spectroscopy of superconducting thin films near the critical temperature
We present a high-resolution microwave spectrometer to measure the
frequency-dependent complex conductivity of a superconducting thin film near
the critical temperature. The instrument is based on a broadband measurement of
the complex reflection coefficient, , of a coaxial transmission
line, which is terminated to a thin film sample with the electrodes in a
Corbino disk shape. In the vicinity of the critical temperature, the standard
calibration technique using three known standards fails to extract the strong
frequency dependence of the complex conductivity induced by the superconducting
fluctuations. This is because a small unexpected difference between the phase
parts of for a short and load standards gives rise to a large
error in the detailed frequency dependence of the complex conductivity near the
superconducting transition. We demonstrate that a new calibration procedure
using the normal-state conductivity of a sample as a load standard resolves
this difficulty. The high quality performance of this spectrometer, which
covers the frequency range between 0.1 GHz and 10 GHz, the temperature range
down to 10 K, and the magnetic field range up to 1 T, is illustrated by the
experimental results on several thin films of both conventional and high
temperature superconductors.Comment: 13 pages, 14 figure
Investigation of superconducting interactions and amorphous semiconductors
Research papers on superconducting interactions and properties and on amorphous materials are presented. The search for new superconductors with improved properties was largely concentrated on the study of properties of thin films. An experimental investigation of interaction mechanisms revealed no new superconductivity mechanism. The properties of high transition temperature, type 2 materials prepared in thin film form were studied. A pulsed field solenoid capable of providing fields in excess of 300 k0e was developed. Preliminary X-ray measurements were made of V3Si to determine the behavior of cell constant deformation versus pressure up to 98 kilobars. The electrical properties of amorphous semiconducting materials and bulk and thin film devices, and of amorphous magnetic materials were investigated for developing radiation hard, inexpensive switches and memory elements
Microwave response of vortices in superconducting thin films of Re and Al
Vortices in superconductors driven at microwave frequencies exhibit a
response related to the interplay between the vortex viscosity, pinning
strength, and flux creep effects. At the same time, the trapping of vortices in
superconducting microwave resonant circuits contributes excess loss and can
result in substantial reductions in the quality factor. Thus, understanding the
microwave vortex response in superconducting thin films is important for the
design of such circuits, including superconducting qubits and photon detectors,
which are typically operated in small, but non-zero, magnetic fields. By
cooling in fields of the order of 100 T and below, we have characterized
the magnetic field and frequency dependence of the microwave response of a
small density of vortices in resonators fabricated from thin films of Re and
Al, which are common materials used in superconducting microwave circuits.
Above a certain threshold cooling field, which is different for the Re and Al
films, vortices become trapped in the resonators. Vortices in the Al resonators
contribute greater loss and are influenced more strongly by flux creep effects
than in the Re resonators. This different behavior can be described in the
framework of a general vortex dynamics model.Comment: Published in Physical Review B 79,174512(2009); preprint version with
higher resolution figures available at
http://physics.syr.edu/~bplourde/bltp-publications.ht
An argon ion beam milling process for native layers enabling coherent superconducting contacts
We present an argon ion beam milling process to remove the native oxide layer
forming on aluminum thin films due to their exposure to atmosphere in between
lithographic steps. Our cleaning process is readily integrable with
conventional fabrication of Josephson junction quantum circuits. From
measurements of the internal quality factors of superconducting microwave
resonators with and without contacts, we place an upper bound on the residual
resistance of an ion beam milled contact of 50 at a frequency of 4.5 GHz. Resonators for which only of the
total foot-print was exposed to the ion beam milling, in areas of low electric
and high magnetic field, showed quality factors above in the single
photon regime, and no degradation compared to single layer samples. We believe
these results will enable the development of increasingly complex
superconducting circuits for quantum information processing.Comment: 4 pages, 4 figures, supplementary materia
Zero-bias anomalies on SrLaCuO thin films
High-impedance contacts made on the surface of SrLaCuO
superconducting thin films systematically display a zero-bias anomaly. We
consider two-level systems (TLS) as the origin of this anomaly. We observe that
the contribution of some TLS to the contact resistance is weakened by a
magnetic field. We show that this could result from the increase of the TLS
relaxation rate in the superconducting state, due to its ability to create
pairs of quasiparticles out of the condensate, when located close to the
surface of the film
A broadband microwave Corbino spectrometer at He temperatures and high magnetic fields
We present the technical details of a broadband microwave spectrometer for
measuring the complex conductance of thin films covering the range from 50 MHz
up to 16 GHz in the temperature range 300 mK to 6 K and at applied magnetic
fields up to 8 Tesla. We measure the complex reflection from a sample
terminating a coaxial transmission line and calibrate the signals with three
standards with known reflection coefficients. Thermal isolation of the heat
load from the inner conductor is accomplished by including a section of NbTi
superconducting cable (transition temperature around 8 9 K) and hermetic
seal glass bead adapters. This enables us to stabilize the base temperature of
the sample stage at 300 mK. However, the inclusion of this superconducting
cable complicates the calibration procedure. We document the effects of the
superconducting cable on our calibration procedure and the effects of applied
magnetic fields and how we control the temperature with great repeatability for
each measurement. We have successfully extracted reliable data in this
frequency, temperature and field range for thin superconducting films and
highly resistive graphene samples
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