3M-E-O1 Sep 9 - Morning (10:30-12:30 PM)
Electronics - Microwave and THz devices
10:30 - 11:00 DC-tunable low-pass microwave filter on superconducting nanopatterned Nb microstrips|
DOBROVOLSKIY Oleksandr1, HUTH Michael1
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We report the design and performance of a dc-tunable low-pass microwave filter  on the basis of high-quality Nb  microstrips with uniaxial nanogrooves  affecting the motion of Abrikosov vortices and the microwave loss accosiated with it . The frequency response of the device is reported for the range 300 KHz – 10 GHz and a series of temperatures, magnetic fields, dc current values, and microwave power levels. The forward transmission coefficient S21(f) of the microstrip has a dc-tunable cut-off frequency, whereby the first-order filter roll-offs of 3 dB/octave are attained when the inter-row vortex spacing matches the groove-to-groove distance (matching field). For grooves with a symmetric cross-section the dc-dependent cut-off frequencies in S21(f) nearly coincide for the forward and backward dc current bias, whereas for grooves with an asymmetric cross-section these drastically differ at moderate dc current values. The device operation principle relies upon a crossover from the weakly dissipative response of vortices at low frequencies when they are driven over the grooves, to the strongly dissipative response at high frequencies when they are oscillating within one groove . The filter cutoff frequency corresponds to the vortex depinning frequency, the latter being tunable by the dc bias as it diminishes the pinning effect induced by the focused ion beam-milled washboard-like nanopattern.
 O.V. Dobrovolskiy, M. Huth, submitted.
 O.V. Dobrovolskiy and M. Huth, Thin Solid Films 520, 5985 (2012).
 O.V. Dobrovolskiy, E. Begun, M. Huth, and V.A. Shklovskij, New J. Phys. 14, 113027 (2012).
 O.V. Dobrovolskiy, J. Franke, and M. Huth, Meas. Sci. Technol. 26, 035502 (2015).
 O.V. Dobrovolskiy, M. Huth, and V.A. Shklovskij, Phys. Procedia 36, 7 (2012).
This work was financially supported by the German Research Foundation (DFG) through grant DO 1511/2-4 and conducted within the framework of the NanoSC-COST Action MP1201.
11:00 - 11:15 YBa2Cu3O7-x bicrystal Josephson junctions with high IcRn-products and wide-ranging resistances for THz applications|
IRINA Gundareva1, DIVIN Yuriy2
1Forschungszentrum Juelich, Germany, 2Kotel’nikov IRE RAS, Russia
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High-Tc Josephon junctions have been found promising for new demanding terahertz (THz) applications as detectors, oscillators and Hilbert-transform spectrum analyzers -. Josephson junctions with high characteristic voltages IcRn to guarantie THz Josephson frequencies and junction resistances Rn ranging from subohm values to several hundred ohms, are required for these applications. Low-resistance -tilt high-Tc junctions with high IcRn-values of around 7 mV can be fabricated from rather thick high-Tc epitaxial films . However, to make high-resistance junctions within the same technology one need to optimize the initial stages of thin-film growth. We present the results on structural, electrical and THz characteristics of the -tilt YBa2Cu3O7-x bicrystal Josephson junctions fabricated on NdGaO3 substrates. Surface treatments of the substrates, growth rates and geometry of YBa2Cu3O7-x electrodes have been optimized to develop thin films with long (up to several micrometers) grains and fabricate high-quality Josephson junctions with a very wide range of resistances Rn. It has been found that the IcRn-values of the junctions fabricated on (320) NdGaO3 bicrystal substrates were independent on Rn-values at the range from 0.3 Ohm to 300 Ohm and were equal to (7+/-1) mV. The maximum IcRn-values of 8.5 mV have been reached. Parameters of THz oscillators and detectors based on the developed high-Tc Josephson junctions with high and resistance-independent IcRn–values will be estimated and their optimization will be discussed.
1.Y. Divin, A. Snezhko, M. Lyatti, U. Poppe, V. Pavlovskiy. Terahertz Applications of Hilbert-Transform Spectral Analysis. IEEE Trans. Appl. Supercond., vol. 24, N. 4, 1500807, 2014.
2.Y. Divin, H.K.B. Pandya. Feasibility of ECE measurements using Hilbe.rt-transform spectral analysis. Fusion Science and Technology, vol. 65, N.3, pp. 399-405, 2014.
3.Y. Divin, A. Snezhko, U. Poppe, I. Gundareva, V. Pavlovskiy. Screening of Liquids with Quasioptical High-Tc Josephson Detectors. In: Nanotechnology in the Security Systems. (Eds: J. Bonca, S. Kruchinin; Springer, Dordrecht, 2015) Part II, pp.165-179.
4.Y. Divin, U. Poppe. Towards “ideal” high-Tc Josephson junction: -tilt YBa2Cu3O7-x bicrystal boundary. Phys. Procedia, vol. 36, pp. 42 – 47, 2012.
Authors are thankfull for a support by Grant RSCF #14-19-01164
11:15 - 11:30 Thermal Instability and THz Emission from High Tc Superconductor Bi2Sr2CaCu2O8+d Mesa Structures|
KADOWAKI Kazuo1, KITAMURA Takeo1, WATANABE Chiharu1, SAIWAI Yoshihiko1, SHIBANO Yuuki1, SAKAMOTO Kazuki1, KUBO Hiroyuki1, YAMAMOTO Takashi2, KASHIWAGI Takanari1, MINAMI Hidetoshi1, KLEMM Richard3
1University of Tsukuba, Japan, 2National Institute for Materials Science, Japan, 3University of Florida, United States
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Recehtly, we have developed a new method to measure the temperature distribution of the THz emitting device fabricated from high temperature superconductor Bi2Sr2CaCu2O8+d while the THz electromagnetic waves were emitting by embrocating SiC fine powders uniformly on the surface of the mesa and observing the photoluminescence intensity after a proper calibration of it [1,2]. This method is better than other previous method such as the low temperature scanning laser microscope method  and photopuminescence intensity measurement under UV (ultra-violet) lihgt from some organic chemical complex containing Eu3+ (Eu-TFC: thenoyltrifluoroacetonate) dilutely coated on the surface of the mesa . Our results shows clearly that the local Joule heating is not beneficial for high power emission at all. In order to improve the emission power it is necesarry to remove Joule heat much more efficiently from the mesa device while the THz emission is taking place.
In order to realize it we have recently developed a stand-alone type of mesa structure and tested it to see the performace. It is remarkable that in the stand-alone mesa there is no sign of the hot spot formation even with a few times larger applied voltage to the mesa and much stronger emission power was observed [5,6]. So far, the maximum frequency of 1.6 THz almost continuously from about 0.4 THz and the maximum power of 30 mW were achieved at about 55 K. This remarkable improvement of THz emission characteristics enebles us further to develop THz emitters to work at the liquid nitrogen temperature .
 H. Minami et al., Phys. Rev. B 89 (2014) 054503, see also U. Welp, K. Kadowaki and R. Kleiner, Nat. Photonics 7 (2013) 702.
 C. Watanabe et al., Appl. Phys. Lett. 106 (2015) 042603.
 H. B. Wang et al., Phys. Rev. Lett. 102 (2009) 017006.
 T. M. Benseman et al., Appl. Phys. Lett. 113 (2013) 133902.
 T. Kitamura et al., Appl. Phys. Lett. 105 (2014) 202603.
 T. Kashiwagi et al., Appl. Phys. Lett. 106 (2015) 092601.
 H. Minami et al., submitted to Phys. Rev. Applied.
This work has been carried out in collaboration with Prof. Dr. R. Kleiner's group and Dr. Wai Kwok's group. We greatly appreciate it.
11:30 - 11:45 Experimental Study of Josephson Effects in Nonuniform Nb-based SIS Parallel Junction Arrays|
BOUSSAHA Faouzi1, CHAUMONT Christine1, FERET Alexandre1, VACELET Thibaut2
1Observatoire de Paris, France, 2Observatorie de Paris, France
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We investigated parallel arrays of superconducting tunnel junctions nonevenly distributed in a superconducting microstrip transmission line. The arrays consist of 10, 20 and 40 Superconductor-Insulator-Superconductor (SIS) parallel-connected Nb/AlOx/Nb junctions embedded in Nb/SiO/Nb lines. Such devices are discretized Josephson transmission lines DJTLs in which, from theory, magnetic flux quanta “fluxons” can travel as solitonic waves when a dc current bias and a dc magnetic field are applied. We observed a reproducible series of resonant branches in each device’s I−V curve, at Josephson submillimeter-wave frequencies within the predefined rf bandwidth. The non periodic distribution was optimized to provide rf matching over a large bandwidth 370–520 GHz typically, implying that the plasma resonance of junctions is inductively tuned out over a similar band by the array. These experimental results are all compatible with a fluxon-based resonances interpretation, as in the extensively studied long Josephson junctions yet at higher frequencies. To detect the output power, we also integrated a SIS twin-junction detector to each array. The pumped detector’s I-V characteristic exhibits clearly photon-assisted quasiparticule steps when the arrays are biased upon corresponding Josephson resonances ranging from 370 to 510 GHz. In light of these unique properties, nonuniform DJTLs are promising for submillimeter-wave oscillators and fast electronics applications.
11:45 - 12:00 Josephson effect at THz frequencies in a planar MgB2 junction|
CUNNANE Daniel1, WOLAK Matthaeus2, ACHARYA Narendra2, KAWAMURA Jonathan1, XI Xiaoxing2, KARASIK Boris1
1Jet Propulsion Laboratory, United States, 2Temple University, United States
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Josephson effect is intriguing in MgB2 in view of the complex material energy band structure featuring two distinctive superconducting gaps. Realization of a junction with properties that are mostly determined by the larger s-gap (D = 7 meV) is a tantalizing task as this may lead to THz digital and detector devices. We have developed a process that yields planar tunnel junctions demonstrating strong Josephson behavior up to 2 THz. In this process, a thin (~ 10 nm) microbridge was created in the center of a 100-nm thick MgB2 structure fabricated using the Hybrid Physical-Chemical Vapor Deposition process. At the end of the bridge adjacent to the thick film, additional milling took place using Ar ion beam. A weak-link planar Josephson junction was realized at the interface between thick and thin film. Since the HPCVD film grown on SiC is c-axis oriented the effect of the s-gap on the junction properties was large.
The rest of the MgB2 film with a thick gold layer on top was formed as a planar log-spiral antenna allowing for high frequency (0.05 to 2 THz) measurements. A quasi-optical test setup included an elliptical Si lens with the Josephson antenna-coupled device mounted on its back thus forming a broad band THz detector. The device was tested using monochromatic submillimeter sources in both mixing and direct detection modes. The current-voltage (IV) characteristic of the device demonstrated Shapiro steps corresponding to lower harmonics of the radiation frequency. As a mixer, the device showed good sensitivity, with a double-side band noise temperature being below 1000 K at 600 GHz. Higher order steps were difficult to observe in the IV curve, so the intermediate frequency power was used, which showed much more sensitivity to Shapiro steps. We were able to find steps corresponding to up to 28 harmonics of 90 GHz radiation, to 4 harmonics of 600 GHz radiation, and a single step for 2 THz leading to the conclusion that the theoretical max frequency set by the ICRN product of 5 mV is close to the actual frequency observed. This is the highest frequency Josephson effect yet allowing for low noise mixing reported. Thorough investigation and further optimization of the device is needed in order to fully understand the underlying physics and the high-frequency limit of this material and its implications on other (e.g., digital) devices.
This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautical and Space Administration.
12:00 - 12:15 Simulation of HTS Josephson junction mixers|
PEGRUM Colin1, ZHANG Ting2, DU Jia2, GUO Yingjie Jay3
1University of Strathclyde, United Kingdom, 2CSIRO, Australia, 3University of Technology Sydney, Australia
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CSIRO has developed a range of superconducting Microwave Monolithic Integrated Circuit (MMIC) mixers using step-edge Josephson junctions and on-chip filters, made from YBaCuO on MgO substrates. These have been shown to have outstanding conversion efficiency, dynamic range and linearity. First-generation devices operated typically at 7 to 12 GHz [1, 2] and recently a 30 to 33 GHz Ka device has been demonstrated .
We have developed a representative circuit model and simulation techniques to complement this experimental work. We use mainly Josephson simulators and analyse data in both the time and frequency domains. Thermal noise sources have been included to model realistically devices operating at 40K. Some of our studies also use microwave simulators incorporating a novel Verilog-A Josephson junction model. We have looked at the interactions of junction bias current, local oscillator power and RF input power with conversion efficiency, dynamic range and linearity, for differing values of junction critical current and resistance. Good agreement is found overall with measurements. Our simulation model can be quickly adapted for any Josephson mixer and we believe that it forms a valuable basis for developing future mixers of this type and for understanding some of their observed properties.
 J. Du, T. Zhang, Y. J. Guo and X. W. Sun, A high-temperature superconducting monolithic microwave integrated Josephson down-converter with high conversion efficiency, Appl. Phys. Lett. 102, 212602 (2013).
 J. Du, D. D. Bai, T. Zhang, Y. Jay Guo, Y. S. He and C. M. Pegrum, Optimised conversion efficiency of a HTS
MMIC Josephson down-converter, Supercond. Sci. Technol. 27, 105002 (2014).
 T. Zhang, J. Du, J. Wang, D. D. Bai, Y. Jay Guo and Y. S. He, 30 GHz HTS receiver front-end based on
monolithic Josephson mixer, IEEE Trans Appl. Supercond. 25 1400605 (2015).
12:15 - 12:30 Space Applications of HTS Microwave Filters and Subsystems in China|
HE Yusheng1, SUN Liang1, LI Chunguang1, LI Hong1, ZHANG Xueqiang1, BIAN Yongbo1, WANG Jis1, WANG Xu1, LI Guoqiang1, WU Yun1
1Institute of Physics, Chinese Academy of Sciences, China
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In the past 20 years, various kinds of HTS filters have been designed and successfully applied to many fields including space applications. The most famous one was “High Temperature Superconductivity Space Experiment” (HTSSE) initiated by the Naval Research Laboratory of the United States. Since then, several similar projects have been carried out in many countries. To our knowledge, however, no successful on orbit experiments or space applications of HTS devices and subsystems were reported after HTSSE.
In China, HTS filters for satellite receiver front-end were designed and fabricated by using both double sided YBCO and TBCCO films. Excellent return loss (< -22.5 dB) and extremely high out-of-band rejection (> 110 dB) at certain frequency bands were achieved. The noise figure of the front-end subsystem, constructed by integrating the HTS filter with a low noise amplifier and a stirling cooler, is lower than 0.5 dB at 77 K. These HTS filters and subsystems have passed all space qualification environmental tests including vibration, centrifuge, and shock tests etc. The first Chinese space HTS subsystem was taken into space with a civilian experimental satellite for new technology on October 14, 2012. Data received from the satellite in the past two years show that the HTS filter and subsystem are working on orbit perfectly, manifesting the success of the space experiment.
Another HTS subsystem for the application of deep space exploration have been developed and completed, which is a payload of Chinese first space laboratory and ready for launching in 2016. Novel receivers with both HTS passive and active devices are under consideration and preparation for the applications in planned Chinese on-orbit astronomical observatory or space station after 2020.