Shunichi Arisawa

Hot spots and waves in Bi2Sr2CaCu2O8 intrinsic Josephson junction stacks: a study by low temperature scanning laser microscopy.

Recently, it has been shown that large stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2O8 emit synchronous THz radiation, the synchronization presumably triggered by a cavity resonance. To investigate this effect we use low temperature scanning laser microscopy to image electric field distributions. We verify the appearance of cavity modes at low bias and in the high input-power regime we find that standing-wave patterns are created through interactions with a hot spot, possibly pointing to a new mode of generating synchronized radiation in intrinsic Josephson junction stacks.

Approach for the fabrication of MgB2 superconducting tape with large in-field transport critical current density

The letter reports the fabrication of MgB2 superconducting tape using a flexible metallic substrate as well as its strong pinning force, which was verified by direct measurement of transport critical current density. The tape was prepared by depositing MgB2 film on a Hastelloy tape buffered with an yttria-stabilized-zirconia layer. The Jc of the tape exceeds 105 A/cm2 at 4.2 K and 10 T, which is considered as a common benchmark for magnet application. The Jc dependence on magnetic field remains surprisingly very small up to 10 T, suggesting that the tape has much better magnetic field characteristic than conventional Nb–Ti wires in liquid helium.

d -like symmetry of the order parameter and intrinsic Josephson effects in Bi 2 Sr 2 CaCu 2 O 8 + δ cross-whisker junctions

An intrinsic tunnel junction was made using two Bi 2 Sr 2 CaCu 2 O 8 + Φ Φ single-crystal whiskers. The two whiskers with a cross angle were overlaid at their c planes and connected by annealing. The angular dependence of the critical current density along the c axis is of the d-wave symmetry. However, the angular dependence is much stronger than that of the conventional d wave. Furthermore, the current vs voltage characteristics of the cross-whisker junctions show a multiple-branch structure at any cross angle, indicating the formation of the intrinsic Josephson-junction array.

Synthesis of YNi2B2C thin films by magnetron sputtering

Thin films of YNi2B2C superconductor by the magnetron sputtering technique have been synthesized. The YNi2B2C phase was found to crystallize very uniformly after annealing at 1050 °C in vacuum. The structure was investigated and the electric and magnetic properties were characterized. The films were c‐axis oriented and showed a Tc onset of ∼15 K by both magnetization and resistivity measurements. The results of the critical current measurement suggested the existence of anisotropies of pinning force and an upper critical field Bc2.

Layer-by-layer growth and magnetic properties of Y3Fe5O12 thin films on Gd3Ga5O12

We report on the layer-by-layer growth of epitaxial yttrium-iron-garnet (Y3Fe5O12) thin films on (111) and (110) Gd3Ga5O12 substrates as verified by the intensity oscillations of reflection high energy electron diffraction during pulsed laser deposition. X-ray diffraction indicates pseudomorphic lattice structure with slight expansion along out of plane from cubic one. The saturation magnetization well reproduces the full moment observed for bulk crystals. The crystallographic magnetic anisotropy was also preserved regardless of shape anisotropy in different orientations. Magnetic anisotropy similar to bulk crystals was observed for as-grown films which have not been subject to a postannealing process.

A cross-whiskers junction as a novel fabrication process for intrinsic Josephson junctions

A Bi2Sr2CaCu2O8+δ cross-whiskers junction has been successfully discovered as a novel intrinsic Josephson junction without using any technique for micro-fabrication. Two Bi2Sr2CaCu2O8+δ whisker crystals were placed crosswise on a MgO substrate and heated at 850 °C for 30 min. They were electrically connected at their c-planes. The measurement terminals were made at the four ends of the whiskers. The I-V characteristics of the cross-whiskers junction at 5 K were found to show a clear multiple-branch structure with a spacing of approximately 15 mV, which is a feature of an intrinsic Josephson junction. The critical current density JC was estimated to be 1170 A cm-2. The branch structure was strongly suppressed by a magnetic field above 1 kOe.

Preparation and superconducting properties of extremely thin Bi2Sr2Ca1Cu2Ox ribbon-like films on silver substrates

Abstract We have developed a simple technique for growing ribbon-like single crystalline films of Bi-2212 on Ag substrates. The process is performed under ambient pressure only by heating the Bi-2212 pellet on the edge of the substrates. The ribbons are extremely thin and stuck firmly to the substrates, resulting in the formation of a new type of composite of Bi-2212 ribbons/Ag. The ribbon-like films showed the superconducting transition with the onset temperature of ∼80 K.

Growth of Single-Crystal Ca10(Pt4As8)(Fe1.8Pt0.2As2)5 Nanowhiskers with Superconductivity up to 33 K

Single-crystal Ca(10)(Pt(4)As(8))(Fe(1.8)Pt(0.2)As(2))(5) superconducting (SC) nanowhiskers with widths down to hundreds of nanometers were successfully grown in a Ta capsule in an evacuated quartz tube by a flux method. Magnetic and electrical properties measurements demonstrate that the whiskers have excellent crystallinity with critical temperature of up to 33 K, upper critical field of 52.8 T, and critical current density of J(c) of 6.0 × 10(5) A/cm(2) (at 26 K). Since cuprate high-T(c) SC whiskers are fragile ceramics, the present intermetallic SC whiskers with high T(c) have better opportunities for device applications. Moreover, although the growth mechanism is not understood well, the technique can be potentially useful for growth of other whiskers containing toxic elements.

Cross-Whisker intrinsic Josephson junction as a probe of symmetry of the superconducting order parameter

As a test of the superconducting order parameter, we have developed an intrinsic Josephson junction by the name of cross-whisker junction. This junction was made using two Bi2Sr2CaCu2O8+d single crystal whiskers. Two whiskers were connected at their c planes with various cross-angles. Angular dependence of the critical current densities shows d-wave-like fourfold-symmetry. However, the angular dependence is much stronger than that of the conventional dx2-y2 wave. The Jc shows its smallest value around 45 deg, which suggests that the Josephson penetration depth becomes longer. We have successfully observed a Fraunhofer pattern in the cross-whisker junction with cross-angle 45 deg.

Synthesis of Bi2Sr2CaCu2O8+δ whiskers without oxygen stream

Abstract A synthesis technique of Bi 2 Sr 2 CaCu 2 O 8+ δ single-crystal whiskers was studied. The whiskers were synthesized by heating glassy melt-quenched Bi–Sr–Ca–Cu–O (3:2:2:4 in cationic ratio) plates. The atmospheric condition of the whisker growth, especially oxygen partial pressure and gas flow, was investigated. It was found out that the whisker growth rate shows a maximum at P O 2 =2/3 bar. For the crystalline quality of the whiskers, the airtight condition was found to be useful as compared to the conventional oxygen stream condition. The crystalline quality, especially the straightness and morphology of the surface, could be improved by keeping the growing whiskers under the equilibrium P Bi condition. Over 20-mm-long whisker crystals have been successfully synthesized by choosing the optimum oxygen partial pressure around P O 2 =2/3 bar in the airtight condition.