Resistive Superconducting Quantum Interference Device Research Articles

Numerical Demonstration of Blocking Oscillation in Resistive Superconducting Quantum Interference Devices

Abstract The author numerically demonstrates several features of blocking oscillation in resistive superconducting quantum interference devices (RSQUIDs) including two Josephson junctions. The key for the blocking oscillation is a combination of discrete and continuous flux transfer into/from the RSQUID loop. The discrete flux transfer takes place through the Josephson junctions, while the dissipative element (resistor) in the loop allows the continuous flux transfer. Three features of the blocking oscillation are presented by numerical simulation. Firstly, switching events alternately occur in the two junctions. Next, a finite average voltage is induced in the RSQUID, when the blocking oscillation is synchronized with an external rf signal. Finally, blocking oscillation modes including several intermittent periods are generated in coupled-RSQUIDs.

Average Voltage Measurements of Periodic Blocking Oscillation in Resistive Superconducting Quantum Interference Device Connected to Josephson Transmission Line

Average Voltage Measurements of Periodic Blocking Oscillation in Resistive Superconducting Quantum Interference Device Connected to Josephson Transmission Line

A self-pumped high-temperature superconducting Josephson mixer: Modelling and measurement

We have recently developed a high-temperature superconducting (HTS) Josephson self-pumped mixer with an on-chip heterodyne local oscillator. The device is based on HTS step-edge junction technology and a “resistive-superconducting quantum interference device” (RSQUID) configuration. The heterodyne local oscillator and mixer output are frequency-tunable from below 10 MHz to 5 GHz by a control current. The performance of the autonomous Josephson mixer–local oscillator has been experimentally evaluated in terms of the current-voltage characteristics, intermediate frequency (IF)-tunable bandwidth, operation range, linearity, bias current, and temperature dependence of the IF output (or mixer conversion efficiency). We find the results are in good overall agreement with numerical simulation.

Average Voltage Measurements of Periodic Blocking Oscillation in Resistive Superconducting Quantum Interference Device Connected to Josephson Transmission Line

Blocking oscillation (BO) is a unique operation mode of resistive superconducting quantum interference devices (RSQUIDs). The author presents experimental measurements of periodic BO by means of the average voltage method. Test circuits are fabricated using a Nb/AlOx/Nb integration process. The input/output voltage ratio in an RSQUID, of which the output is connected to a Josephson transmission line (JTL), becomes 2 under appropriate operation conditions. Since the voltage ratio is exactly proportional to the input/output switching frequency ratio, the results demonstrate the periodic BO, in which the numbers of switching during one period are 2 and 1 in the input and output junction, respectively.

SQUIDS mix it up

Researchers in Australia have reported the use of a high temperature superconducting resistive superconducting quantum interference device (HTS R-SQUID) for the first time as a self-pumped mixer in the GHz frequency range. This opens the way for potential innovations in wireless receiver technology, where many HTS passive components with superior performance have already been employed.

Numerical Demonstration of Relaxation Oscillation in a Resistive Superconducting Quantum Interference Device With Two Nonhysteretic Josephson Junctions

The author numerically demonstrates that a resistive superconducting quantum interference device (RSQUID) with two nonhysteretic Josephson junctions works as a relaxation oscillator. Sequential switching of the Josephson junctions transfers positive and negative flux quanta in the RSQUID loop one by one. Differently from a conventional two-junction superconducting quantum interference device, the dissipative RSQUID loop does not maintain the quantized flux, and hence, finite flux can be accumulated in the RSQUID loop during sequential switching of the Josephson junctions. When the accumulated flux reaches a critical value, the corresponding loop current prevents subsequent junction switching. That is, the oscillation stops. After the loop current decays, sequential switching of the junctions resumes. In addition to the waveforms of relaxation oscillation, dependence of relaxation oscillation on device parameters is presented.

Noise temperature and linewidth of high-temperature-superconducting heterodyne gigahertz oscillators

A method for the generation of stable, widely tunable heterodyne oscillations by means of a high-temperature-superconducting resistive superconducting quantum interference device is described. The details of the fabrication techniques, electrical characteristics, operating temperatures and frequency range of 100MHz–2GHz, are reported. The noise temperatures of several devices, made and tested in different laboratories, are estimated and the linewidths of the heterodyne oscillations are compared with theoretical values.

Characterization of YBCO/Au/YBCO resistors for HTS Josephson noise thermometry

It has been proposed that an absolute thermometer based on the linewidth broadening of the Josephson oscillation could be realized in the temperature range 10 K to 50 K with the use of high-temperature-superconducting resistive superconducting quantum interference devices (HTS R-SQUIDs). Although this technique has been successfully demonstrated with LTS devices in the temperature region below 1 K, there are unresolved problems which have so far prevented its translation to higher operating temperatures. A crucial component of a resistive SQUID noise thermometer is the shunt resistor, which is required to have a value <0.1 m/spl Omega/. The often excessive and unpredictable contact resistance between normal metal and HTS superconducting thin films has up to now hindered the successful implementation of an HTS resistive SQUID. YBCO-Au-YBCO shunt resistors with suitable resistance values of /spl sim/20 /spl mu//spl Omega/ have recently been manufactured and their characteristics under cryogenic operating conditions have been measured using the Josephson frequency-voltage relationship.

Integrated thin-film dc RSQUIDs for noise thermometry

Integrated thin-film dc RSQUIDs (Resistive Superconducting QUantum Interference Devices) have been developed that significantly simplify noise thermometer operation. We show theoretically that the main equations for noise thermometry deduced for rf RSQUIDs can also be applied to dc RSQUIDs. Our dc RSQUIDs can at least be operated down to 0.04 K. Between 0.14 and 5.9 K the measured noise temperature agrees with the temperature of calibrated reference thermometers. We investigate the errors and uncertainties of a dc RSQUID noise thermometer, in particular errors due to excess noise. A model for excess noise and its impact on the noise temperature is presented and shown to be in agreement with the measurements.

The current–voltage characteristics of the resistive direct current superconducting quantum interference device

Partly resistive superconducting quantum interference devices (RSQUIDs) are used in noise thermometry in the liquid helium temperature range. Here we analyze one type of RSQUID that has not been thoroughly investigated until now: the direct current biased with two Josephson junctions and a resistive part connected in series with the junctions and closed by a superconducting ring. The resistive shunted model of the Josephson junctions is used for the analysis. Two cases of the RSQUID ring inductance were analyzed: (i) negligibly small and (ii) small but finite inductance. The expressions for the low frequency output signal, the current–voltage (I–V) characteristics, and the current flowing through the resistive part are obtained. In the dependence of the output frequency versus the dc current passed through the resistive part often an offset is observed experimentally. This phenomenon can be explained as an influence of an asymmetry in the critical currents of the junctions.

Thin-film resistive SQUIDS

Different all thin-film partly resistive superconducting quantum interference devices (RSQUIDs) for noise thermometry in the liquid helium temperature range were designed and investigated. Three different types of RSQUID were realised: (i) dc RSQUID, (ii) rf RSQUID, and (iii) RSQUID with two quantization loops (double RSQUID). Shunted tunnel junctions were used as weak links. The resistive parts have been made as a Cu thin film combined with Nb thin films either as a sandwich or a planar element. The devices using a rf pump have integrated rf coupling coils. Resistances of the resistive parts in the range from 2.69 /spl mu//spl Omega/ to 246 /spl mu//spl Omega/ were obtained. The output signal was /spl ap/50 /spl mu/V for the dc RSQUIDs, up to 80 /spl mu/V for the rf RSQUIDs, and up to 1.2 mV for the double RSQUIDs. The linear dependences of the output signal frequency versus a dc current passed through the resistive part were observed up to 40 MHz. The double RSQUIDS described have a clear advantage in the output signal compared to the other RSQUIDs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and fabrication of thin-film resistive SQUIDs

A partly resistive superconducting quantum interference device, or, RSQUID, is a device utilizing the nonstationary Josephson effect. The resistive part of the device makes it possible to apply a voltage to the Josephson junctions and, in this way, to convert it into frequency. The transconductance ratio of this conversion is defined by the physical constants: 1/o0 = 2e/h (o0 is the flux quantum). Five different types of thin-film RSQUIDs are described in this paper. They are: an rf RSQUID with an rf pump and one Josephson junction, a dc RSQUID with dc bias and two Josephson junctions, and three topologically different double RSQUIDs with an rf pump, two Josephson junctions and two quantization loops. All five types were successfully fabricated. The resistive part of all devices was an S-N-S sandwich with Nb as the superconductor (S) and Cu as the normal metal (N). Such a design of the resistive part sets its resistance on the order of a few tens of μΩ.

A resistive superconducting quantum interference device with two quantization loops

A simplified theoretical analysis and experimental investigations of a partially resistive superconducting quantum interference device with two quantization loops have been performed. The advantage of this device is an extremely large output signal. It is shown that the output signal oscillates with a period determined by the nonstationary Josephson relation. This device was experimentally compared to the dc resistive superconducting quantum interference device used as a test structure.

A resistive SQUID with two quantization loops

We introduce a SQUID (superconducting quantum interference device) consisting of two Josephson junctions incorporated into a partly resistive loop. An additional superconducting loop is connected to the junctions in parallel and inductively coupled to the tank circuit supplied by an rf current source. It is experimentally shown that this configuration can be used as a voltage-to-frequency converter. The voltage to be converted is applied to the resistive part of the first loop. In comparison to the known resistive SQUIDs, this device has the advantage of a larger output signal due to using two quantization loops. The design of the thin-film device and the experimental results are reported. Output signal values in order of up to 1 mV have been obtained.

Impedance of radio-frequency-biased resistive superconducting quantum interference devices.

We have measured with high accuracy (100 ppm) and high precision (5--10 ppm) the impedance of a rf-driven resistive superconducting quantum interference device (SQUID) as a function of the amplitude and frequency of the radio-frequency (rf) bias, as a function of the current bias, and as a function of several other circuit parameters. We have developed the coupled differential equations for the resistive SQUID and for the rf tank circuit. The fit of the solutions of these equations to the data for nonhysteretic junctions is excellent. We were unable to develop solutions for the hysteretic case and thus simply present examples of typical data obtained in order to illustrate the differences with the nonhysteretic case. The relationship of this study to noise thermometry using resistive SQUID's is indicated.

Direct heterodyne detection of 245-GHz radiation using the internal narrowband oscillations of a resistive dc SQUID

A current controlled voltage across a resistive section in a double Josephson junction interferometer (dc resistive superconducting quantum interference device) maintains a difference voltage between the junctions to generate a narrowband oscillatory signal at the beat frequency νq of the individual junction frequencies. This internal oscillation was used to directly down-convert a signal at 246 GHz to a very low (&amp;lt;1 MHz) intermediate frequency.

Tunable narrow-linewidth oscillations and current-voltage characteristics of a resistive dc SQUID

The output voltage of a dc superconducting quantum interference device (SQUID) containing a resistive section Rs oscillates at a frequency νq =Vs/ φ0 (φ0=flux quantum) when a current controlled voltage Vs is maintained across Rs. These oscillations have been observed from ∼10−1 to 1011 Hz, using Rs values ranging from ∼10−10 to ∼10−3 Ω in low inductance (∼10−10 H) point contact SQUID loops. At high frequencies, they manifest themselves in the dc current-voltage characteristics by inducing extra current steps.