• 한국초전도학회:학술대회논문집
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• v.10
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• pp.21-21
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• 2000

The Josephson Plasma resonance in single crystalling Bi2Sr2CaCu2O8 has been investigated at a microwave frequency of 35 GHz in a cavity resonator. A sharp resonance is observed in a perpendicular oscillating magnetic field. The former is independent of the sample dimension, shile the latter shift to higher field as the sample size L is reduced, and it disappears when L becomes smaller than the critical length. The longitudinal plasma mode is a Nambu-Goldston mode in a superconductor, the experimental distinction between the longitudinal and the transverse mode leads to the conclusion that the existence of the Nambu-Goldston mod as predicted by Anderson was experimentally confirmed by direct observation of the Josephson plasma resonance with longitudinal excitations. The finite gap found in Josephson plasma resonance also provides a direct proof of the Anderson-Higgs mechanism within the context of the spontaneously broken phase symmetry of the Gauge-field theory in a superconductor.

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.56-56
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• 2004

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.9-14
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• 2000

We report on the novel nonequilibrium nlicrowave emission from quasiparticle-injected high-Tc superconductors. The phenomena have been observed for the current-injected YBCO/I/Au or BSCCO/I/Au thin-film tunnel junctions and BSCCO single-crystal intrinsic Josephson mesa junction samples. For the thin-film tunnel junctions, the emitted radiation appears as broadband. For the intrinsic BSCCO mesa samples, the radiation appears as three different modes of emissions depending on the bias point in the hysteretic current-voltage characteristics; Josephson-emission, nonequilibrium broad emission and sharp coherent microwave emission. The results were interpreted by the Josephson plasma excitation model due to quasiparticle injection.

• Progress in Superconductivity
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• v.6 no.1
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• pp.52-55
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• 2004

The inductive coupling theory in serially stacked $Bi_2$$Sr_2$$CaCu_2$$O_{8+x}$ intrinsic Josephson junctions predicts that the lattice structure of the Josephson vortices along the c axis gradually changes from the triangular to the rectangular lattice with increasing the vortex velocity. This lattice transition appears as voltage jumps or sub-branch splitting in the Josephson vortex-flow region of current-voltage characteristics (IVC). We report the IVC in external magnetic fields from 2 to 4 T. The stack, with the lateral size of 1.4${\times}$15 $u\m^2$, was fabricated by using the double-side cleaving technique. The sub-branches in the Josephson vortex-flow region, corresponding to a plasma propagation mode in serially coupled intrinsic Josephson junctions, were also observed in the range of 2∼4T. Switching from one branch to another in Josephson vortex-flow region suggests the structural transition of the moving Josephson vortex lattice.

• 한국초전도학회:학술대회논문집
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• v.16
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• pp.47-47
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• 2006

• 한국초전도학회:학술대회논문집
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• v.15
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• pp.44-44
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• 2005

• Progress in Superconductivity
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• v.4 no.2
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• pp.104-108
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• 2003

We have measured the transport properties of $Bi_2$$Sr_2$$CaCu_2$$O_{8+d}$ (BSCCO) intrinsic Josephson junction mesa. Transport measurements with current flow along the c-axis, perpendicular to the layer of mesa showed multi-branch structures on the current-voltage characteristics. For single intrinsic junctions, the microwave radiation appears in the form of three different modes of oscillations, which include Josephson emission, nonequilibrium broad emission and sharp coherent microwave emission. Mutual phase interactions between two-mesas structures of BSCCO intrinsic Josephson junctions were studied. The results were explained within the framework of the Josephson plasma excitation model due to quasiparticle injection.n.

• Progress in Superconductivity
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• v.5 no.1
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• pp.9-12
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• 2003

We observed the splitting of the fluxon-flow branches in the current-voltage characteristics of serially stacked intrinsic Josephson junctions (IJJs) formed in $Bi_2$$Sr_2$$CaCu_2$$O_{ 8＋x}$ single crystals in the long-junction limit. Stacks of IJJs were sandwiched between two Au electrodes deposited on the top and the bottom of the stack using the ‘double-side cleaving technique’. In all the samples studied, the branch splitting started occurring for a dense fluxon configuration around 2 T and became more distinct in a higher magnetic field range. This observation can be explained in terms of switching between different Josephson fluxon modes in resonance with the collective plasma oscillations induced by both inductive and capacitive coupling between stacked IJJs. This is the first detailed and quantitative identification of the coherent flux-flow modes in stacked..

• Progress in Superconductivity
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• v.3 no.1
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• pp.49-55
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• 2001

Josephson junction arrays were fabricated by DC magnetron sputtering, self-aligning and reactive ion etching technique. The Al native oxide, formed by thermal oxidation, was used as the tunneling barrier of Nb/$Al-A1_2$$O_3$Nb trilayer. The arrays have 2,000 Josephson junctions with the area of $14\mu\textrm{m}$ $\times$ $46\mu\textrm{m}$. The gap voltages were in the range of 2.5 ~2.6 mV and the spread of critical current was $\pm$11~14%. When operated at 70~94 ㎓, the arrays generated zero-crossing steps up to 2.1~2.4 V. To improve transmission of microwave power and prevent diffusion of oxygen into Nb ground-plane while depositing $SiO_2$dielectric, we applied a plasma nitridation process to the Nb ground-plane. The microwave power was well propagated in Josephson junction arrays with nitridation. The difference in microwave transmission 7an be interpreted by the surface impedance change depending on nitridation.

• Progress in Superconductivity
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• v.8 no.2
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• pp.138-142
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• 2007

We observed discrete fluxon-flow resonance steps in high magnetic fields in a stack of Josephson junctions with lateral size of $1.5{\times}17{\mu}m^2$. The measurement sample was prepared by sandwiching a stack of $Bi_2Sr_2CaCu_2O_{8+x}$ intrinsic Josephson junctions between two Au electrodes by using the double-side-cleaving technique. This technique allowed us to isolate the intrinsic Josephson junction structures from the inductive interference of the basal stack. The resonance steps observed are in good agreement with the collective Josephson fluxon dynamics that are in resonance with the plasma oscillation modes inside the stacked Josephson junctions.