Eiji Kume

Direction-oriented quasiparticle injection and microwave emission in an ErBa2Cu3Oy superconductor

We report the anisotropic microwave emission properties of ErBa2Cu3Oy/insulator/Au (S/I/N) tunnel junctions due to the direction-oriented quasiparticle injection. Two types of samples with different S/I/N tunnel junction geometries are prepared: one allows the quasiparticle injection mainly along the c axis and the other only into the ab plane. The results show the presence of strong anisotropic behavior of microwave emission according to the direction of quasiparticle injection.

Nonequilibrium Microwave Emission from DC-Biased High Tc YBa2Cu3O7-y Junctions

We report the observation of microwave emission from dc-biased high Tc Au/insulator/YBa2Cu3O7-y junctions, which provides a novel method of generating broad-band microwaves. The microwave intensity is typically of the order of subpicowatts, and increases almost linearly with the increase of junction current and vanishes as the bath temperature approaches Tc. The observed effect is not similar to the Josephson effect and may be interpreted in terms of the nonequilibrium dynamics involving Cooper pairs and quasiparticles.

On-chip spectroscopic detection of terahertz radiation emitted from a quasiparticle-injected nonequilibrium superconductor using a high-Tc Josephson junction

We report a novel sensitive terahertz spectroscopy in which both the electromagnetic generator and the detector are fabricated on the same chip. The radiation emitted from a tunnel-injected nonequilibrium high temperature (high-Tc) YBa2Cu3O7−y superconductor is detected by a high-Tc bicrystal Josephson junction. The observed data are converted to the spectral data by means of inverse Hilbert transformation. The resultant emitted spectra exhibit a broad peak around 1 THz, extending up to 2.5 THz. The relation to the Josephson plasma emission is discussed.

Growth of Single Phase Bi2Sr2CaCu2Ox Whiskers Using Optimized Starting Compositions for Glassy Precursors

Single phase Bi2Sr2CaCu2Ox whiskers were grown by optimized starting compositions for glassy precursors. The most optimal starting composition ratio and the composition after the whisker growth were found to be Bi:Sr:Ca:Cu:Al=0.96:1.10:0.37:1.21:0.61 and Bi2.25Sr2.09Ca0.87Cu2.00Ox, respectively. From the results of R–T characteristics, it was determined that there was no intergrowth of the Bi2Sr2Ca2Cu3Ox phase.

Growth of High-Quality Single-Phase Bi2Sr2CaCu2Ox Whiskers by a New Growth–Melt–Regrowth Method

High-quality and large single-phase Bi2212 whiskers are grown by a new growth–melt–regrowth method. The average composition of the Bi2212 whiskers and the maximum size of single-crystal domains are Bi2.15Sr2.08Ca0.90Cu2.00Ox and 0.5 µm × 88 µm × 2 mm, respectively. The results of X-ray diffraction analysis and I–V characteristic measurement indicate that the crystallinity of the obtained Bi2212 whiskers is excellent.

Observation of Nonequilibirum Microwave Emission from dc-Biased High Tc YBa2Cu3O7-y Junctions

We report the observation of microwave emission from dc-biased high Tc Au/insulator/YBa2Cu3O7-y junctions, which provides a novel method to generate broad-band microwaves. The microwave intensity increases nearly linearly with the increase of junction current and diminishes away as the bath temperature approaches Tc. The observed effect is not of Josephson nature and may be interpreted by the nonequilibrium dynamics involving Cooper pairs and quasiparticles.

Josephson plasma emission from tunnel-injected nonequilibrium high-T c superconductors

We report on the novel nonequilibrium microwave emissions from quasiparticle-injected high-Tc superconductors. The phenomena have been observable for the current-injected YBa2Cu3O7- y(YBCO)/I/Au or Bi2Sr2CaCu2Oy(BSCCO)/I/Au thin- film tunnel junctions and BSCCO single-crystal mesa samples. For the thin-film tunnel junctions, the emitted radiation appears as broadband. The different emission characteristics between the YBCO and BSCCO tunnel junctions strongly suggest the possibility of Josephson plasma emission. On the other hand, for the mesa samples, the radiation appears as three different modes depending on the bias point in the hysteretic current-voltage characteristics: Josephson self-emission, nonequilibrium broad emission and sharp emission. The latter two emission are identified as Josephson plasma emission.

Microwave Emission from Quasiparticle-injected Intrinsic Junctions

The microwave emissions from the quasiparticle-injected Bi2Sr2CaCu2Oy (BSCCO) intrinsic Josephson junctions along the c-axis are reported. Using a superheterodyne mixer techinque, three different modes of microwave emissions corresponding to the different branches of the hysteretic I — V characteristics of the intrinsic junction are found. At the low bias voltage range, the conventional Josephson self-emission is observable, whereas, at the high bias voltage range, the two novel microwave emissions due to the nonequilibrium effect are recorded; incoherent broadband emissions and a sharp coherent microwave emission. We interpret these two emissions in terms of Josephson plasma emission.

Microwave emission due to anisotropic quasiparticle injection into an ErBa/sub 2/Cu/sub 3/O/sub y/ superconductor

We report the observation of microwave emission and the dc measurements on tunnel injection of quasiparticles into a ErBa/sub 2/Cu/sub 3/O/sub y/ (EBCO) thin film using the samples with antenna geometry which are nearly free from the parallel overlapping effect of the injector current and the thin film current. The injector consists of two EBCO/insulator/Au (S/I/N) gate junctions. The samples were fabricated by lift-off photolithography technique. The microwave emission intensity from the junction was measured under the condition of broadband non-resonant matching using a superheterodyne radiometric receiver at frequencies f/sub REC/=36 GHz and 47 GHz. The detected microwave emission power increased nearly linearly with the injection current. The emitted power was greater for the higher receiving frequency. The observed maximum emitted broad band spectrum power at frequency f/sub REC/=47 GHz was about 10 pW for an integrating time of 1 sec. The phenomenon is discussed in terms of the nonequilibrium dynamics together with the ionic nature of oxide superconductor.