• Progress in Superconductivity
• /
• v.7 no.1
• /
• pp.11-16
• /
• 2005

Coupling of non-linear oscillators have long been an interesting problem for physicists. The coupling phenomena have been frequently observed in Josephson junction series array, which have been used for Josephson voltage standard. Interestingly pronounced self-generation effect has been found during recent development of Josephson arrays for programmable Josephson voltage standard. But the coupling effect between the self-generations is not fully understood yet. We present harmonically approximated analytical solutions for coupled self-generations in the Josephson arrays, i.e., Superconductor-Insulator-Normal metal-Insulator-Superconductor (SINIS) array, externally shunted Superconductor-Insulator-Supercondctor (es-SIS) array, Superconductor-Normal metal-Superconductor (SNS) array. We find that the coupling between the self-generated Josephson oscillations through microwave transmission line plays critical role in microwave property of the Josephson array.

• Progress in Superconductivity
• /
• v.13 no.1
• /
• pp.47-51
• /
• 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
• /
• v.5 no.1
• /
• pp.5-8
• /
• 2003

We studied the effect of spin injection on tunneling conduction properties of intrinsic Josephson junctions formed in $Bi_2$$Sr_2$$CaCu_2$$O_{ 8＋x}$ single crystals. properties of an identical stack (10${\times}$5.0${\times}$0.030 $\mu\textrm{m}^3$) of intrinsic Josephson junctions were compared for the bias current injected through Au and Co electrodes. The suppression of the superconducting gap in the $_2$ double layers and the interlayer Josephson critical current was manifested in the tunneling current-voltage characteristics of the stacks. This effect appears to be caused by the pair breaking associated with spin-polarized carriers injected from the Co electrode into the $Bi_2$$Sr_2$$_2$O$CaCu_{ 8＋x}$ single crystal. This study may provide valuable information on clarifying the mechanism of high- $T_{c}$ superconductivity.y.y.

• Progress in Superconductivity
• /
• v.1 no.2
• /
• pp.110-114
• /
• 2000

We have investigated the Josephson vortex dynamics in $Bi_2Sr_2CaCu_2O{8+\delta}$ intrinsic Josephson junctions subjected to a magnetic field parallel to $CuO_2$ planes. We investigated mesas with $40\times40{\mu}m^2$ in size and containing 6 and 20. intrinsic junctions. The zero field I-V characteristics exhibited a typical hysteretic, multi-branched nature of the intrinsic Josephson effect. At high magnetic fields (H>1.5 T), I-V characteristics showed flux flow steps. The Swihart velocity obtained from this observation was about $4.2\times10^5$ m/s, which was the lowest mode electromagnetic wave velocity of N coupled stack. The experimental I-V curves fitted well into the simple model of Cherenkov radiation including Ohmic and non-linear dissipation terms. This suggests that the dissipation mechanism of Josephson vortex be due to both Cherenkov radiation and quasiparticle tunneling current.

• Progress in Superconductivity
• /
• v.9 no.2
• /
• pp.140-145
• /
• 2008

We report on the Josephson vortex dynamics in $Bi_2Sr_2CaCuO_{8+\delta}$ natural Josephson junctions by c-axis tunneling measurements. Beside the quasiparticle branches in the current-voltage characteristics, a new set of multiple branches, referred to as Josephson-vortex-flow branches (JVFBs), are observed. The JVFBs emerge in an in-plane magnetic field above $H_0\;=\;{\Phi}_0/{\gamma}s^2$ and show highly hysteretic behavior, which can be explained in terms of the recently proposed dynamic-phase-separation model. In this work we examined the effect on the JVFBs by the presence of pancake vortices generated as the external magnetic field was applied slightly tilted from the in-plane direction. JVFBs were found to become larger and prominent with increasing pancake vortex density as the tilt angle increased, which were presumably caused by slowing down of a Josephson vortex lattice in the presence of pancake vortices.

• Progress in Superconductivity and Cryogenics
• /
• v.4 no.1
• /
• pp.1-3
• /
• 2002

Single Josephson junctions, which are of cross type, of $50 ${\mu}{\textrm}{m}$ {\times} 50 ${\mu}{\textrm}{m}$$ were fabricated under several oxidation conditions to Investigate controllabilities of critical current density (Jc) with the standard KRISS processes. Considering that the self-field effect suppresses the observed critical current (Ice) at high Jc region, we could reasonably estimate Jc values from I-V observations. The dependence of the obtained Jc as a function of exposure, which is equal to pressure (P) times time (t), was well fitted to a curve of Jc ~ (Pt)-0.34. The maximum Jc value at the controllability margin was found to be 3 kA/cm$^2$with the current equipment set up.

• 한국초전도학회:학술대회논문집
• /
• v.13
• /
• pp.28-28
• /
• 2003

• Progress in Superconductivity
• /
• v.3 no.1
• /
• pp.1-4
• /
• 2001

Interface-engineered junctions with $YbBa_2$$Cu_3$$O_{7}$ as the counter electrode were demonstrated. The junctions exhibited excellent Josephson characteristics with a Josephson critical current ($I_{c}$) ranging from 0.1 mA to 8 mA and a magnetic field modulation of the $I_{c}$ exceeding 80% at 4.2 K while maintaining complete c-axis orientation of the counter-electrode layer. The$ 1\sigma$ spreads in $I_{c}$ for junctions with an average $I_{c}$ of 1-2 mA were 5-8% for 16 junctions within a chip, and 9.3% for a 100-junction array. Our dI/dV measurements suggest that a theoretical approach taking into account both a highly transparent barrier and the proximity effect is required to fully understand the Junction characteristics.ristics.

• 한국초전도학회:학술대회논문집
• /
• v.9
• /
• pp.223-228
• /
• 1999

We have investigated the microwave properties of a high-T$_c$. superconducting Josephson junction by Shapiro step measurements. A Josephson junction was fabricated on the bicrystal MgO substrate using pulsed laser deposition method. We have measured Shapiro steps in the I-V characteristics under the irradiation of 1.36 cm wavelength up to 45 K and found inclined current steps above 50 K. In order to understand these results, we introduced an additional resistance connected in series to RSJ model. Using this modified RSJ model, we could explain the inclined current steps as a result of superposition of the junction and an additional resistance above certain temperatures. Also, we presented the received power of the Josephson junction above 50 K.

• Progress in Superconductivity and Cryogenics
• /
• v.19 no.4
• /
• pp.18-21
• /
• 2017

We report a method for improving heat exchange between cryo-cooled large-power-dissipation devices and liquid cryogen. Micro-machined monolithic heat sinks were fabricated on a high integration density superconducting Josephson device, and studied for their effect on cooling the device. The monolithic heat sink showed a significant enhancement of cooling capability, which markedly improved the device operation under large dc- and microwave power dissipation. The detailed mechanism of the enhancement still needs further modeling and experiments in order to optimize the design of the heat sink.