• Progress in Superconductivity
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• v.13 no.1
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• pp.47-51
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• 2011

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.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.6-9
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• 2019

Developing a gate-tunable, scalable, and topologically-protectable supercurrent qubit and integrating it into a quantum circuit are crucial for applications in the fields of quantum information technology and topological phenomena. Here we propose that the nano-hybrid supercurrent transistors, a superconducting quantum analogue of a transistor, made of topological insulator nanowire would be a promising platform for unprecedented control of both the supercurrent magnitude and the current-phase relation by applying a voltage on a gate electrode. We believe that our experimental design will help probing Majorana state in topological insulator nanowire and establishing a solid-state platform for topological supercurrent qubit.

• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.5-8
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• 2016

We report on the fabrication and measurement results of the electrical transport properties of superconductor-normal metal-superconductor (SNS) weak links, made of PbIn superconductor and Au metal. The maximum supercurrent reaches up to ${\sim}6{\mu}A$ at T = 2.3 K and the supercurrent persists even at T = 4.7 K. Magnetic field dependence of the critical current is consistent with a theoretical fit using the narrow junction model. The superconducting quantum interference device (SQUID) was also fabricated using two PbIn-Au-PbIn junctions connected in parallel. Under perpendicular magnetic field, we clearly observed periodic oscillations of dV/dI with a period of magnetic flux quantum threading into the supercurrent loop of the SQUID. Our fabrication methods would provide an easy and simple way to explore the superconducting proximity effects without ultra-low-temperature cryostats.

• 한국초전도학회:학술대회논문집
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• v.15
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• pp.34-34
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• 2005

• Progress in Superconductivity
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• v.7 no.2
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• pp.167-173
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• 2006

Coated conductors suitable for the fabrication of persistent mode high $T_c$ magnets are suggested and the fabrication method of persistent mode magnets using coated conductor are demonstrated. Persistent current was observed in a small piece of coated conductor. Closed loop of coated conductor with a diameter of around 1 em was successfully prepared and was cooled with a magnetic field of about 500 Gauss in order to induce supercurrent. Coated conductor with a $I_c$ of 100 A/cm-width was used for the preparation of closed loop of coated conductor. Persistent current was confirmed by measuring the magnetic field generated from closed loop of coated conductor by using Gauss meter. Magnetic field of 4.4 Gauss was detected from the supercurrent of closed loop of coated conductor. It shows that superconducting joint of coated conductor is not a prerequisite for the construction of persistent mode magnets. It is thought that this work opens the possibility to use coated conductor for the construction of persistent mode high $T_c$ magnets for MRI, NMR and magnetic separation applications.

• Progress in Superconductivity
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• v.9 no.2
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• pp.136-139
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• 2008

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.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.11-15
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• 2022

We conducted numerical calculations to obtain the critical current as a function of the magnetic flux through the topologically trivial and non-trivial superconducting quantum interference devices (SQUIDs), with varying the capacitive and inductive couplings of Josephson junctions (JJs). Our calculation results indicate that a nontrivial SQUID is almost indistinguishable from trivial SQUID, considering the effective capacitance coupling. When the SQUID contains 2π- and 4π-periodic supercurrents, the periodicity of the current-flux relation can be distinguished from the purely trivial or nontrivial SQUID cases, and its difference is sensitive to the relative ratio between the topologically trivial and nontrivial supercurrents. We believe that our calculation results would provide a practical guide to quantitatively measure the portion of the topologically nontrivial supercurrents in experiments.

• Progress in Superconductivity
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• v.6 no.1
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• pp.13-18
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• 2004

High-.ate in-situ$ YBa_2$Cu$Cu_3$$O_{7-x}$ (YBCO) film growth was demonstrated by means of the electron beam co-evaporation. Even though our oxygen pressure is low, ∼$5 ${\times}$10^{-5}$ Torr, we can synthesize as-grown superconducting YBCO films at a deposition rate of around 10 nm/s. Relatively high temperatures of around 90$0^{\circ}C$ was necessary in this process so far, and it suggests that this temperature at a given oxygen activity allows a Ba-Cu-O liquid formation along with an YBCO epitaxy. Local critical current density shows a clear correlation with local resistivity. Homogeneous transport properties with a large critical current density ($4 ∼ 5 MA/\textrm{cm}^2$ at 77K, 0T) are observed in top faulted region while it is found that the bottom part carries little supercurrent with a large local resistivity. Therefore, it is possible that thickness dependence of critical current density is closely related with a topological variation of good superconducting paths and/or grains in the film bodies. The information derived from it may be useful in the characterization and optimization of superconducting films for electrical power and other applications.

• Progress in Superconductivity
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• v.3 no.1
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• pp.28-30
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• 2001

We studied the flux-flow current-voltage characteristics of microwave-generated fluxons formed in serially stacked intrinsic Josephson junctions fabricated on$ HgI_2$-intercalated $Bi_2$$Sr_2$$CaCu_2$O/8+x/(Bi2212) single crystals. With increasing the irradiation power of 73$\square$76 GHz microwave, the supercurrent branch became resistive and split into multiple sub -branches. Each sub-branch represented a specific mode of collective motion of Josephson fluxons. We also observed similar branch splitting In a mesa prepared on an underdoped Bi2212 single crystal in a static magnetic field.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.6-10
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• 2022

We report on the fabrication and measurements of metallic Josephson junctions (JJs) consisting of Au nanoribbon and NbTi superconducting electrodes. The maximum supercurrent density in the junction reaches up to ~ 3×10⁵ A/cm² at 2.5 K, much larger than that of JJ using single-crystalline Au nanowire. Temperature dependence of the critical current exhibits an exponential decay behavior with increasing temperature, which is consistent with a long and diffusive junction limit. Under the application of a magnetic field, monotonous decrease of the critical current was observed due to a narrow width of the Au nanoribbon. Our observatons suggest that NbTi/Au/NbTi JJ would be a useful platform to develop an integrated superconducing quantum circuit combined with the superconducting coplanar waveguide and ferromagnetic π junctions.