Masahiro Akinaga

Electronic structure studies of the Bi2212 system by polarised X-ray absorption measurement

Polarised X-ray absorption (XAS) measurements have been made on high-quality superconducting Bi2Sr2CaCu2Os+y (Bi2212) single crystals to investigate the microscopic electronic structure in the normal and superconducting state of the system. The Cu L 3 XAS results led us to conclude that either there are no holes of 3dzz symmetry, or if any, they are insignificant in number. On the other hand, the O K XAS results show the presence of a significant density of p~ symmetry orbitals for itinerant holes. An increase in the 3d9_L/3d 9 ratio estimated from the Cu L 3 XAS measurements was observed while going from the normal to the superconducting state of the system. The results are discussed in the light of the structural distortions taking place below T c.

Surface Acoustic Waves in High-Tc Superconducting Thin Films on Piezoelectric PbTiO3 Films

To generate surface acoustic waves (SAW) and to fabricate substrates for superconducting Bi-compound film, piezoelectric PbTiO3 films with preferred c-axis orientation were prepared on MgO (100) substrates by the rf-sputtering method. By using an interdigital electrode fabricated on PbTiO3 film for generation and detection of SAW, it has been confirmed that SAW with the frequency of 192 MHz are propagated on PbTiO3 film/MgO substrate, as-deposited Bi-compound film/PbTiO3/MgO substrate and heat-treated superconducting Bi-compound film/PbTiO3/MgO substrate. The temperature dependence of the SAW attenuation coefficient has been investigated below room temperature in detail, especially in the neighborhood of the superconducting transition temperature, and found to exhibit almost monotonic decreasing behavior with decreasing temperature.

A simple preparation of superconducting MgB2 thin films by composite: target sputtering system

Abstract As-grown superconducting MgB 2 thin films were fabricated by very simple RF sputtering method. A two-component target comprising of many small slices of B on a Mg disk was used. The films were deposited onto polished single crystal sapphire or SrTiO 3 substrates at rather low temperatures ranging from 100 to 110 °C. Five samples on SrTiO 3 substrate and one on sapphire showed zero resistivity at about 15 K and onset at about 20 K with measuring the resistance versus temperature ( R – T curves). The overall feature of the transport phenomena was very different from the measured feature in the prepared MgB 2 bulk sample with much grain boundaries. The temperature dependence of the critical current and the transition behavior in current versus voltage curves ( I – V curve) were much BCS-type.

Reentrant transition in tetragonal superconductor CaLaBaCu3Oy

Abstract The tetragonal CaLaBaCu 3 O y and LnSrBaCu 3 O y (Ln = Dy, Eu, Gd) samples were prepared and their transport properties were measured in detail. The reentrant transition below usual transition temperature were confirmed for the samples, CaLaBaCu 3 O y , GdSrBaCu 3 O y and EuSrBaCu 3 O y which are phenomenologically similar to those in magnetic superconductors.

Surface acoustic waves in high-Tc superconducting thin films

Piezoelectric PbTiO3 films with preferred c-axis orientation were fabricated on MgO substrates by RF-sputtering method. By using a fabricated interdigital electrode, surface acoustic waves (SAWs) with a frequency of 192 MHz were propagated on PbTiO3 film/MgO substrate and on superconducting Bi(Pb)2Sr2Ca2Cu2Oy film/PbTiO3/MgO substrate. The temperature dependence of the SAW attenuation coefficient was investigated below room temperature.

Critical current in tetragonal superconductor CaLaBaCu3Oy

Abstract Tetragonal CaLaBaCu 3 O y (CLBCO) samples with several different oxygen contents were prepared by changing the annealing temperature or annealing time in O 2 . Oxygen-rich samples showed normal transport properties with homogeneous oxygen content. On the other hand, rather oxygen-less samples with inhomogeneous concentration showed unusually reentrant superconductivity like “magnetic superconductors”.

Temperature dependence of the critical current in bulk sample and thin film of Bi-compound superconductors

Abstract Temperature dependences of the critical current in Bi(Pb)2Sr2CaCu2Oy films prepared on MgO (100) and SrTiO3 (100) by rf-sputtering, Bi2Sr2CaCu2Oy films prepared by MOCVD on MgO (100) and Bi(Pb)2Sr2Ca2Cu3Oy bulk samples were measured in detail. For the bulk sample, the dependence was similar to that in a typical SIS junction. On the other hand, for the case of CVD-grown films without grain boundaries, it is suggestive to be due to SNS junction. The sputtered films with many grains it showed the intermediate behavior between SNS- and SIS-type.

Thermodynamic fluctuation in the Bi(Pb, Sb)-Sr-Ca-Cu-O superconductors

Measurements of the excess conductivity above the superconducting transition for 110-K phase of the Bi(Pb, Sb)-Sr-Ca-Cu-O compound are reported. The data are very well described in terms of the classic theory of thermodynamic fluctuations in a two-dimensional superconductor.

Possible high Tc superconductivity and large fluctuation effect in Nb3Ge films

Abstract The electrical resistivity ϱ( T ) of RF sputter-deposited Nb 3 Ge films has been investigated in detail in the neighborhood of the transition temperature. After cooling to below room temperature, many samples exhibited a semiconductive type of increase in the resistivity before undergoing the transition to superconductivity. These films have very large resistivity in the normal state (ϱ n =10 3 -10 5 μΩ cm) and show fairly high onset temperatures. The maximum value of the onset temperature T c-on reaches 32 K. On the other hand, the films with rather small resistivity exhibited a metallic behavior in the normal state. However, the fluctuation effect on the electrical conductivity starts from a higher temperature than the usual onset temperature where we can see a clear drop of the resistivity. The films were examined by EPMA and SEM to reveal the correlation between the superconductive properties and the microstructure.

Thin film growth of high-Tc superconductor by infrared-ray irradiation

Abstract The heat treatment of superconducting Bi-compounds has been performed by using infrared-ray irradiation. By local heat treatment using the ray irradiation and a slit, we succeeded in growing 2212 thin film with 1 mm width between deposited SAW (surface acoustic waves) interdigital electrodes pair separated in 5 mm without damage to them.