Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A47: Superconducting Devices and Applications |
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Sponsoring Units: DCMP Chair: Neda Foroozani, Washington University Room: Mile High Ballroom 4F |
Monday, March 3, 2014 8:00AM - 8:12AM |
A47.00001: Thickness dependence of superconducting properties in NbN thin films Matthew Burton, Douglas Beringer, Melissa Beebe, Elizabeth Visosky, David Brantley, Shaan Sharma, Kaida Yang, Ale Lukaszew Thin film NbN is a promising material currently researched for improvements in superconducting radio frequency (SRF) technology and applications. At present, bulk niobium SRF accelerating cavities suffer from a fundamental upper limit in maximally sustained accelerating gradients; however, a scheme involving multi-layered superstructures consisting of superconducting-insulating-superconducting (SIS) layers has been proposed to overcome this fundamental material limit of 50 MV/m [1]. The SIS multi-layer paradigm is reliant upon implementing a thin shielding material with a suitably high Hc1 which may prevent early field penetration in a bulk material layer and consequently delay the high field breakdown. It has been predicted that for thin superconducting films --- thickness less than the London penetration depth ($\sim$200 nm in the case of NbN) --- the lower critical field Hc1 will be enhanced with decreasing thickness. Thus, NbN thin films with a high Hc1 value are prime candidates for such SIS structures. Here we present our study on the structure and superconducting properties of a series of epitaxial NbN thin films and correlate the effects of film thickness on the lower critical field, Hc1. \\[4pt] [1] A. Gurevich, Appl. Phys. Lett., 88, 012511 (2006). [Preview Abstract] |
Monday, March 3, 2014 8:12AM - 8:24AM |
A47.00002: Quality factors of plasma resonances in Josephson junction chains Thomas Wei{\ss}l, Bruno K\"{u}ng, \'{E}tienne Dumur, Alexey Feofanov, C\'{e}cile Naud, Olivier Buisson, Wiebke Guichard One dimensional Josephson junction arrays (1DJJA's) have found application in a variety of superconducting circuits. They are used as tunable inductors in microwave resonators, as non-linear elements in parametric amplifiers and large inductors in quantum bits. 1DJJA's show internal resonances that are caused by the finite self capacitance of the superconducting islands. The self-capacitance couples the plasma resonances of the individual junctions leading to plasma modes extended over the entire array[1]. We present microwave measurements of plasma modes of a chain containing 200 squids with $E_j/E_c \approx 10$. Three of the plasma modes can be accessed directly in our experiment. By two-tone spectroscopy we observe the 14 lowest modes[2]. We observe quality factors that are strongly power dependent down to low signal levels. This power dependence is analyzed taking into account the low critical current of our arrays. The signal observed in the two-tone detection is higher than one would expect for a cross-Kerr coupling. We show that this sensitivity is due to the fact that the quality factor of a mode depends on the number of photons in all other modes in the array. [1] N. A. Masluk et al., Phys. Rev. Lett. 109, 137002 (2012). [2] T. Wei{\ss}l et al. (in preparation). [Preview Abstract] |
Monday, March 3, 2014 8:24AM - 8:36AM |
A47.00003: Ginzburg-Landau modeling of Nano-SQUIDs John Kirtley, Dibyendu Hazra, Klaus Hasselbach, Olivier Buisson NanoSQUIDs are micron-sized Superconducting Quantum Interference Devices with narrow (50 nm) sized constrictions as weak links. They are used for, e.g., studying switching dynamics in magnetic nanoparticles and high spatial resolution magnetic microscopy. When the constriction dimensions become comparable to or larger than the superconducting coherence length, the current-phase relations become non-sinusoidal, reducing the flux modulation depth and increasing the thermally activated flux noise. We have numerically solved the Ginzburg-Landau (GL) equations for the nanoSQUID geometry to obtain current-phase relations, the dependence of critical current on magnetic flux, and the thermally activated escape rates. We predict NanoSQUIDs with short coherence lengths to have critical current distribution widths, and therefore flux noises, proportional to T$^{1/2}$, as opposed to tunnel junction SQUIDs, which are proportional to T$^{2/3}$. Our GL simulations predict that the ultimate noise performance of Al nanoSQUIDs, with their longer coherence lengths, should be better than Nb nanoSQUIDs, with suspended bridge Al/Nb nanoSQUIDs intermediate between the two. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A47.00004: Batch fabrication of nano-SQUIDs for the single spin detection Lei Chen, Xixi Liu, Zhen Wang, Xiaoming Xie The superconducting quantum interference device (SQUID) is well known as a super sensitive spin detector. The minimal detectable spin number of a SQUID is proportional to the size of its superconducting loop. Hence, nano-SQUIDs consisted of two constricted junctions are possible to be scaled down towards the single spin detection. Here, we are going to present our current research progress on a top-down batch fabrication process of NbN nano-SQUIDs. Ultra-thin NbN film of high quality can be grown on MgO substrate epitaxially. The spin sensitivity of such thin film nano-SQUID can be further enhanced by coupling spins directly to the constricted junctions. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A47.00005: A tunable microstrip SQUID amplifier for the Axion Dark Matter eXperiment (ADMX) Sean O'Kelley, Elan Weingarten, Michael Mueck, Jorn Hansen, John Clarke We present a microstrip SQUID amplifier (MSA) with an octave of tunability for use in the ADMX collaboration. The axion dark matter candidate is detected via conversion to a microwave photon stimulated by an apparatus consisting of an 8 tesla magnet and a cryogenically cooled high-Q tunable microwave cavity. The microwave photon frequency is a function of the unknown axion mass, so the detector must scan over a broad frequency range. An MSA is constructed by flux-coupling a resonant microstrip to a resistively-shunted SQUID biased into the voltage state. We demonstrate a gain exceeding 20 dB with a tunability of nearly one octave from 415 MHz to 800 MHz. Tunability is achieved by terminating the microstrip with a low inductance GaAs varactor that operates at cryogenic temperatures, allowing a variable reflected phase of nearly 0 to $\pi $ at the end of the microstrip, and thus a standing wave tunable from nearly $\lambda $/2 to $\lambda $/4. [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A47.00006: Fabrication and study of ultrathin MgB$_{2}$ films for hot electron bolometer applications Matthaeus Wolak, Teng Tan, Daniel Cunnane, Boris Karasik, Xiaoxing Xi Hot electron bolometers (HEBs) based on superconducting thin films have already been demonstrated and successfully employed in the past. Magnesium diboride (MgB$_{2}$) has a potential to replace the currently used materials due to its higher critical temperature (39 K) and shorter intrinsic electron-phonon relaxation time. The high $T_{c}$ of MgB$_{2}$ could lead to advanced HEBs with higher operating temperatures, while the short relaxation time could help achieve a higher intermediate frequency bandwidth. In order to fabricate MgB$_{2}$ based HEBs, high-quality thin films with thicknesses of about 10 nm are required. We fabricated ultrathin MgB$_{2}$ films of 10 nm and less in our lab using the hybrid physical chemical vapor deposition (HPCVD) technique. The fabrication, characterization, and feasibility of these films for hot electron bolometer applications will be presented. [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A47.00007: Electron heating in superconducting cuprate heterostructures and its application for advanced sensing Andrei Sergeev, Bo Wen, Roman Yakobov, Sergey Vitkalov, Boris Karasik Low electron density in superconducting LaSrCuO heterostructures containing quasi-two dimensional CuO layers leads to strong reduction of the interaction between electrons and thermal phonons and simultaneously to substantial enhancement of the electron-electron interaction. This hierarchy of kinetic processes provides very effective quasiparticle multiplication and slow quasiparticle relaxation and recombination. Strong heating of quasiparticles in the superconducting and resistive states makes these superconducting nanomaterials to be very attractive for various sensing applications based on electron heating. These nanostructures allow for the managing of quasiparticle relaxation rate from low values determined by the electron-phonon relaxation to high values in short devices with out-diffusion electron cooling. Therefore, LSCO heterostructures are very interesting for applications in sensitive resistive detectors, kinetic inductance detectors, and wideband mixers. We experimentally determined key material parameters, design corresponding sensors and evaluated their parameters. [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A47.00008: MgB$_{2}$ thin films for SRF application Teng Tan, Matthaeus Wolak, Narendra Acharya, Ke Chen, Xiaoxing Xi Superconducting RF (SRF) cavities are usually fabricated from bulk niobium (Nb), a material which is thoroughly studied and approaching its limits. Magnesium diboride (MgB$_{2})$ has a higher $T_{c}$ of 39 K, a lower residual resistivity of \textless 0.1 $\mu\Omega$ cm (at 42 K), and a higher thermodynamic critical field $H_{c}$ value comparing with Nb. These properties imply that a MgB$_{2}$-coated SRF cavity would work at a higher temperature with a lower energy dissipation. However, the lower critical field $H_{c1}$ of MgB$_{2}$ is low and vortex dissipation above $H_{c1}$ can lead to degradation of the quality factor and a low RF breakdown field. In this work, we report an enhancement of $H_{c1}$ in both c-axis oriented epitaxial and polycrystalline MgB$_{2}$ thin films. The value of $H_{c1}$ (5 K) was increased from 60 mT in a 300 nm-thick MgB$_{2}$ film to 180 mT when the MgB$_{2}$ layer thickness was 100 nm in both cases. The microwave properties of the MgB$_{2}$ films were characterized as well by using the dielectric resonator technique. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A47.00009: Doping optimization for ultra-high quality factor superconducting niobium cavities for particle acceleration Alexander Vostrikov, Alexander Romanenko, Anna Grassellino, Young-Kee Kim Increasing quality factor of the fundamental mode in superconducting radio frequency (SRF) niobium cavities is vital for development of the future particle accelerator facilities, i.e. LCLS-II, Project X, ERLs, and ADS for nuclear energy and waste transmutation, since it directly affects the dissipated power in cavity walls. It has been discovered that doping of certain concentration of nitrogen into the surface of superconducting niobium significantly improves the quality factor of SRF cavities. We report the results of the nitrogen doping optimization guided by diffusion model and present two surface treatment procedures that allow achieving optimal value of nitrogen concentration at the surface of cavity: one with electropolishing required, another one without it. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A47.00010: Tunneling rates of electron pumping in the R-SINIS transistor Vladimir Bubanja We consider the influence of the electromagnetic fluctuations on the transport properties of a hybrid single electron transistor, consisting of superconducting electrodes and a normal-metal island, when operated as a turnstile. We derive the analytic expressions for the rates near the thresholds of single electron tunneling, Andreev reflection, and Cooper-pair--electron cotunneling processes. These results show that the dissipative on-chip impedance suppresses the rates of the undesirable higher-order tunneling processes much stronger than the single electron tunneling which can therefore be utilized to increase the accuracy of such a device in quantum metrological applications. \\[4pt] [1] J.P. Pekola, J.J. Vartiainen, M. M\"{o}tt\"{o}nen, O.-P. Saira, M. Meschke, D.V. Averin, Nat. Phys. 4, 120 (2008).\\[0pt] [2] D.V. Averin, J.P. Pekola, Phys. Rev. Lett. 101, 066801 (2008).\\[0pt] [3] V. Bubanja, Phys. Rev. B 83, 195312 (2011).\\[0pt] [4] V. Bubanja, submitted. [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A47.00011: Novel Schemes for Cuprate Nanodevice Fabrication Nick Litombe, Anthony Bollinger, Ivan Bozovic, Jenny Hoffman We have fabricated La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO) nanodevices using high resolution electron beam writing coupled with photolithographic techniques. We characterized the patterned films with electrical transport measurements using a variable temperature cryostat. We report on the search for additional, non-deleterious fabrication schemes to yield pristine and small cross-section cuprate nanodevices. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A47.00012: Superconducting Memristors Massimiliano Di Ventra, Sebastiano Peotta In his original work Josephson [Phys. Lett. 1, 251 (1962)] predicted that a phase-dependent conductance should be present in superconductor tunnel junctions. This effect attracted considerable attention in the past but is difficult to detect, mainly because it is hard to single it out from the background pair current. Here, we propose to isolate it by using a two-junction interferometer where the junctions have the same critical currents but different conductances. The pair current is completely suppressed when the magnetic flux in the loop is half of a flux quantum and the device is characterized by a pure phase-dependent conductance. According to the theory of nonlinear circuit elements this is in fact an ideal voltage-controlled memristor. Possible applications of this memristive device are memories and neuromorphic computing within the framework of ultrafast and low-energy superconducting digital circuits. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A47.00013: A terahertz imaging system using high $T_{c}$ superconducting oscillators fabricated from the Bi2212 single crystals T. Kashiwagi, K. Nakade, Y. Saiwai, H. Minami, T. Kitamura, C. Watanabe, K. Ishida, S. Sekimoto, K. Asanuma, T. Yasui, Y. Shibano, K. Kadowaki, M. Tsujimoto, T. Yamamoto, B. Markovic, J. Mirkovic We have developed a terahertz (THz) oscillator based on high $T_{c}$ superconductor of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$(Bi2212) single crystals\footnote{L. Ozyuzer \textit{et al.}, Science \textbf{318} (2007) 1291.} and have succeeded in developing 30$\mu $W level of output power,\footnote{S. Sekimoto \textit{et al.}, Appl. Phys. Lett. \textbf{130} (2013) 023703.} which is continuous, monochromatic as well as stable at frequencies between 0.3 $\sim$ 1.0 THz.\footnote{T. Kashiwagi \textit{et al.}, Jpn. J. Appl. Phys. \textbf{51} (2012) 010113.} Recently, for the purpose of application use of our THz oscillator, we have developed the reflection type of the imaging system in addition to the transmission imaging system reported previously.\footnote{M. Tsujimoto \textit{et al.}, J. Appl. Phys. \textbf{111} (2012) 123111.} We will show the details of the system and the images obtained here as practical example and compared those with previous results. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A47.00014: SLUG Microwave Amplifiers for Scalable Superconducting Qubit Readout Shaojiang Zhu, David Hover, Guilhem Ribeill, Ted Thorbeck, Robert McDermott We describe a phase-insensitive microwave linear amplifier based on the Superconducting Low-inductance Undulatory Galvanometer (SLUG). The amplifier is well suited to the high fidelity quantum nondemolition measurement of superconducting qubits in a circuit quantum electrodynamics architecture. The amplifier has achieved instantaneous bandwidth greater than 400 MHz and system added noise of order one quantum in the GHz frequency range; moreover, the SLUG -1 dB compression point is around -95 dBm, about two orders of magnitude higher than that achieved with typical Josephson parametric amplifiers. We describe efforts to increase instantaneous bandwidth toward 1 GHz and discuss prospects for simultaneous measurement of multiple superconducting qubits using frequency-domain multiplexing with a broadband SLUG amplifier. [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A47.00015: Temperature and Current Bias Dependence of All-MgB$_{2}$ RSFQ Toggle Flip Flop Circuits Elias Galan, Daniel Cunnane, Ke Chen, Xiaoxing Xi We have fabricated and tested Rapid Single Flux Quantum Toggle Flip Flop (TFF) Circuits using self-shunted MgB$_{2}$/MgO/MgB$_{2}$ Josephson Junctions with a single ground layer to reduce parasitic inductance. The MgB$_{2}$ film and electrodes were deposited using HPCVD, and the MgO barrier was deposited using DC reactive sputtering. We highlight the circuits' operation dependence on current bias and temperature which show operation from 8 K to 33 K. The highest attained operating speed is 240 GHz at 10 K. These results demonstrate the versatile temperature range and speed of MgB$_{2}$ based circuits and devices. [Preview Abstract] |
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