Showing papers by "Myung-Ho Bae published in 2003"

Microwave distribution in stacked Bi2Sr2CaCu2O8+x intrinsic Josephson junctions in a transmission-line geometry

Abstract: The microwave distribution inside a rectangular stack (15 μm×0.72 μm×60 nm) of Bi2Sr2CaCu2O8+x intrinsic Josephson junctions (IJJs) was studied. The stack was microfabricated into a transmission-line geometry, with a-few-hundred-nm-thick Au layers deposited on the top and bottom of the stack. The microwave distribution was monitored by measuring the anomalous suppression of the tunneling critical current of the IJJs with varied microwave power at frequencies in the W band. This technique can provide valuable information on the microwave transmission modes inside the sandwiched stack of IJJs, which is utterly important for the high-frequency device applications using IJJs, such as fluxon-flow THz oscillators.

Microwave distribution in stacked Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ intrinsic Josephson junctions in a transmission-line geometry

Abstract: The microwave distribution inside a rectangular stack (15 $\mu$m$\times$0.72 $\mu$m$\times$60 nm) of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ intrinsic Josephson junctions (IJJs) was studied. The stack was microfabricated into a transmission-line geometry, with a few hundred nm thick Au layers deposited on top and bottom of the stack. The microwave distribution was monitored by measuring the anomalous suppression of the tunneling critical current of the IJJs with varied microwave power at frequencies in the W band. This technique can provide valuable information on the microwave transmission modes inside the sandwiched stack of IJJs, which is utterly important for the high-frequency device applications using IJJs, such as fluxon-flow THz oscillators.

Collective dynamics of Josephson fluxons in Bi2Sr2CaCu2O8+δ intrinsic junctions

Abstract: The dynamic characteristics of Josephson fluxons in naturally stacked intrinsic Josephson junctions in Bi2Sr2CaCu2O8+δ single crystals were studied experimentally. The Josephson fluxons were generated either by irradiating microwaves or by applying dc magnetic fields in parallel with the junction planes. In the presence of a finite tunneling bias current the fluxons are driven along the junctions in resonance with the excitation modes of Josephson plasma and thus exhibit a variety of dynamic characteristics. Thus in the flux-flow state of fluxons in both cases above, for a relatively low vortex density, sub-branch splitting of the ‘supercurrent’ branch in the current–voltage (I–V) characteristics was observed, which corresponded to different plasma excitation modes. For a higher vortex density, on the other hand, all the quasiparticle branches merged into a single non-hysteretic I–V curve which exhibited step-like kink features, very similar to the recently predicted ones corresponding to different moving fluxon patterns. The detailed agreement with the theoretical prediction, however, is yet to be confirmed.

Collective motion of Josephson vortices in Bi2Sr2CaCu2O8+δ mesa structures

Abstract: We studied the collective motion of Josephson vortices generated by microwave irradiation and by an external dc magnetic field applied in parallel with the planes of intrinsic junctions of Bi 2 Sr 2 CaCu 2 O 8+ δ single crystals. In both cases, for a low vortex density and driving current, splitting of the ‘supercurrent’ branch corresponding to different plasma excitation modes was observed in the current–voltage characteristics (IVC). For a high vortex density in fields beyond 3–4 T, the IVC merged into a single non-hysteretic curve with kinks, similar to those arising from the theoretically proposed structural transformation of moving vortex patterns.