Introduction to IEC Standardization for Superconducting Sensors and Detectors

Ohkubo, M. The Korean Superconductivity Society 2012 Progress in superconductivity Vol.14 No.2

Superconducting sensors and detectors have been applied to many fields or beginning to enter the maturing stage. The applications spread over a wide range of fields such as radio telescope, medical examination, quantum information, contamination inspection, materials analysis, etc. For users of the superconducting devices as well as developers, we have to avoid confusion of naming, graphical circuit symbols, and measurement methods for device performance. We are trying to formulate international standards under the International Electrotechnical Commission - Technical Committee 90 (IEC-TC90), which is responsible for superconductivity. The sensors and detectors to be considered are divided into two groups: coherent sensors (SQUID, SIS mixers, etc.) and direct detectors (TES, STJ, MKID, SSPD, etc.).

Brief Review on Iron-based Superconductors: are There Clues for Unconventional Superconductivity?

Oh, Hyung-Ju,Moon, Ji-Soo,Shin, Dong-Han,Moon, Chang-Youn,Choi, Hyoung-Joon The Korean Superconductivity Society 2011 Progress in superconductivity Vol.13 No.2

Study of superconductivity in layered iron-based materials was initiated in 2006 by Hosono's group, and boosted in 2008 by the superconducting transition temperature, $T_c$, of 26 K in $LaFeAsO_{1-X}F_X$. Since then, enormous researches have been done on the materials, with $T_c$ reaching as high as 55 K. Here, we review briefly experimental and theoretical results on atomic and electronic structures and magnetic and superconducting properties of FeAs-based superconductors and related compounds. We seek for clues for unconventional superconductivity in the materials.

Pseudogap behavior in interlayer tunneling spectroscopy in $Bi_{2}Sr_{2}CaCu_{2}O_{8+x}$

배명호,최재현,이후종,Bae Myung-Ho,Choi Jae-Hyun,Lee Hu-Jong The Korean Superconductivity Society 2005 Progress in superconductivity Vol.7 No.1

A pseudogap in the normal-state quasiparticle density of states of $high-T_c$ superconductors has been revealed in many different kinds of experiments. The existence of the pseudogap and the superconducting gap, and the correlation between them has attracted considerable attention because they are believed to be a key to understanding the mechanism of the $high-T_c$ superconductivity. The interlayer tunneling spectroscopy, excluding the surface-dependent effect, is one of the most accurate means to examine the electron spectral characteristics both in the superconducting and the normal states. In this study, a new constant-temperature intrinsic tunneling spectroscopic technique, excluding the overheating effect using the in-situ temperature monitoring combined with the digital proportional-integral-derivative control, is introduced. The implication on the $high-T_c$ superconductivity of the detailed temperature dependencies of the observed spectral weight in $Bi_{2}Sr_{2}CaCu_{2}O_{8+x}\;high-T_c$ material for overdoped and underdoped levels is discussed.

Two-band effect in superconducting parameters and their anisotropies of $MgB_2$ single crystals

강병원,김헌정,이현숙,이성익,Kang, Byeong-Won,Kim, Heon-Jung,Lee, Hyun-Sook,Lee, Sung-Ik The Korean Superconductivity Society 2007 Progress in superconductivity Vol.8 No.2

We have studied superconducting parameters of $MgB_2$ single crystals from reversible magnetization measurements with the magnetic field both parallel and perpendicular to the c-axis of the crystals. The temperature dependence of the London penetration depth, ${\lambda}_{ab}{^{-2}}(T)$, obtained from the Hao-Clem analysis on reversible magnetization, shows a clear discrepancy from single-band theories. It is also found that the anisotropies of the London penetration depth, ${\gamma}_{\lambda}$, slowly increases with temperature while the anisotropy of the upper critical field, ${\gamma}_H$, decreases with temperature. These behaviors are in sharp contrast with the behavior of superconductors with a single band. The temperature dependence of ${\lambda}_{ab}{^{-2}}$, and the opposite temperature dependences of ${\gamma}_{\lambda}\;and\;{\gamma}_H$ can be well explained with the theory of the two-band superconductivity.

Gate-tunable Supercurrent in Graphene-based Josephson Junction

정동찬,이길호,도용주,이후종,Jeong, D.,Lee, G.H.,Doh, Y.J.,Lee, H.J. The Korean Superconductivity Society 2011 Progress in superconductivity Vol.13 No.1

Mono-atomic-layer graphene is an interesting system for studying the relativistic carrier transport arising from a linear energy-momentum dispersion relation. An easy control of the carrier density in graphene by applying an external gate field makes the system even more useful. In this study, we measured the Josephson current in a device consisting of mono-layer graphene sheet sandwiched between two closely spaced (~300 nm) aluminum superconducting electrodes. Gate dependence of the supercurrent in graphene Josephson junction follows the gate dependence of the normal-state conductance. The gate-tunable and relatively large supercurrent in a graphene Josephson junction would facilitate our understanding on the weak-link behavior in a superconducting-normal metal-superconducting (SNS) type Josephson junction.

Investigation on the Commercialization Issues of Resistive Type Superconducting Fault Current Limiters for Electric Networks

Park, Tae-Gun,Lee, Sang-Hwa,Lee, Bang-Wook The Korean Superconductivity Society 2009 Progress in superconductivity Vol.11 No.1

Among the various types of fault current limiters, superconducting fault current limiters could be the most preferable choice for high voltage electric power systems owing to the remarkable current limiting characteristics of superconductors. But, there have been no commercial superconducting fault current limiters which were installed into actual electric power systems until these days due to some remained technical and economical problems. Thus, in order to promote the development and application of the superconducting fault current limiters into real field, it is essential to understand the power utilities’ requirements for their networks and also suitable test method and some specifications should be prepared. This paper focuses on the matters of test requirements and standardization issues that should be prepared for commercialization of superconducting fault current limiters. The unique current limiting characteristics of superconducting fault current limiters were investigated and related other standards including circuit breakers, transformers, reactors, power fuse, and fused circuit breakers were compared to setup the basis of novel specification of superconducting fault current limiters. Furthermore, required essential test procedures for superconducting fault current limiters were suggested.

Superconducting Junctions of InAs Semiconductor Nanowires

Doh, Yong-Joo,Franceschi, Silvano De,van Dam, Jorden A.,Bakkers, Erik P. A. M.,Kouwenhoven, Leo P. The Korean Superconductivity Society 2008 Progress in superconductivity Vol.9 No.2

InAs semiconductor nanowires can provide a promising platform to integrate superconducting quantum circuit, which exploits tunable supercurrent under the operation of gate voltage. We report temperature and magnetic field dependence of the nanowire superconducting junctions, which is in agreement with the proximity-effect theory of superconductor-normal metal-superconductor weak link. Superconducting coherence length of the InAs nanowire is estimated from the fit and magnetic-field dependence of the critical current and the subgap structure of dI/dV is discussed as well.

Superconducting Strip Ion Detectors for Time-of-flight Mass Spectrometer

Zen, N.,Suzuki, K.,Shiki, S.,Ukibe, M.,Koike, M.,Casaburi, A.,Ejrnaes, M.,Cristiano, R.,Ohkubo, M. The Korean Superconductivity Society 2012 Progress in superconductivity Vol.14 No.2

Superconducting detectors are promising as ion detectors for time-of-flight mass spectrometers (TOF MS). They can achieve mass-independent detection efficiency even for macromolecular bombardments, because output signals are produced through the deposited kinetic energy at ion impact instead of secondary electron emission that is the ion detection mechanism of conventional microchannel plate (MCP) detectors or secondary electron multipliers (SEM). Among the superconducting detectors, the superconducting strip ion detectors (SSIDs), which consist of several hundreds of superconducting lines with a width of a few hundreds nm and a thickness of a few tens of nm, have a fast response time of less than 1 ns. Inherently, the response time of SSIDs is determined by kinetic inductance, so that it was difficult to realize a fast SSID with a large detection area. However, we succeeded in realizing the detector size up to $5{\times}5mm^2$ without response time degradation by using a parallel configuration.

Fundamental Metrology by Counting Single Flux and Single Charge Quanta with Superconducting Circuits

Niemeyer, J. The Korean Superconductivity Society 2002 Progress in superconductivity Vol.4 No.1

Transferring single flux quanta across a Josephson junction at an exactly determined rate has made highly precise voltage measurements possible. Making use of self-shunted Nb-based SINIS junctions, programmable fast-switching DC voltage standards with output voltages of up to 10 V were produced. This development is now extended from fundamental DC measurements to the precise determination of AC voltages with arbitrary waveforms. Integrated RSFQ circuits will help to replace expensive semiconductor devices for frequency control and signal coding. Easy-to-handle AC and inexpensive quantum voltmeters of fundamental accuracy would be of interest to industry. In analogy to the development in the flux regime, metallic nanocircuits comprising small-area tunnel junctions and providing the coherent transport of single electrons might play an important role in quantum current metrology. By precise counting of single charges these circuits allow prototypes of quantum standards for electric current and capacitance to be realised. Replacing single electron devices by single Cooper pair circuits, the charge transfer rates and thus the quantum currents could be significantly increased. Recently, the principles of the gate-controlled transfer of individual Cooper pairs in superconducting A1 devices in different electromagnetic environments were demonstrated. The characteristics of these quantum coherent circuits can be improved by replacing the small aluminum tunnel Junctions by niobium junctions. Due to the higher value of the superconducting energy gap ($\Delta_{Nb}$ = $7\Delta_{Al}$), the characteristic energy and the frequency scales for Nb devices are substantially extended as compared to A1 devices. Although the fabrication of small Nb junctions presents a real challenge, the Nb-based metrological devices will be faster and more accurate in operation. Moreover, the Nb-based Cooper pair electrometer could be coupled to an Nb single Cooper pair qubit which can be beneficial for both, the stability of the qubit and its readout with a large signal-to-noise ratio..

A Single-Flux-Quantum Shift Register based on High-$T_c$ Superconducting Step-edge Josephson Junctions

Sung G.Y.,Choi, C.H.,Suh J.D.,Han, S. K.,Kang, K.Y.,Hwang, J.S.,Yoon, S.G.,Jung, K.R.,Lee, Y.H.,Kang, J.H.,Kim, Y.H.,Hahn, T.S. The Korean Superconductivity Society 1999 Progress in superconductivity Vol.1 No.1

We have fabricated and tested a simple circuit of the rapid single-flux-quantum(RSFQ) four-stage shift register using a single layer high-$T_c$ superconducting (HTS) $YBa_2Cu_3O_{7-x}$ (YBCO) thin film structure with 9 step-edge Josephson junctions. The circuit includes two read superconducting quantum interference devices(SQUID) and four stages. To establish a robust HTS RSFQ device fabrication process, we have focussed on the reproducible process of sharp and straight step-edge formation as well as the ratio of film thickness to step height, t/h. The spread of step-edge junction parameters was measured from each 13 junctions with t/h=1/3, 1/2, and 2/3 at various temperatures. We have demonstrated the simplified operation of the shift register at 65 K.