D.H. Ha

High-pressure synthesis of the homogeneous infinite-layer superconductor Sr0.9La0.1CuO2

Abstract We synthesized the electron-doped infinite-layer superconductor Sr 0.9 La 0.1 CuO 2 in the high-pressure condition of about 4 GPa. Structural and low-field magnetization studies demonstrated that the superconducting properties of our samples were far superior to any reported results.

Fabrication of YBCO/STO/YBCO multilayer by PLD

Abstract We have measured the electrical properties of YB 2 Cu 3 O y /SrTiO 3 /YB 2 Cu 3 O y (YBCO/STO/YBCO) multilayers prepared by the pulsed laser deposition method under the various deposition conditions of insulating STO layer. Superconducting properties of both YBCO layers are sensitively affected by the deposition temperature, T s , of insulating STO layer. T c of lower YBCO layer is decreased due to the oxygen loss during the deposition of STO layer, but the superconductivity of upper YBCO layer is severely deteriorated due to the poor crystalline quality for low T s . However, we have successfully fabricated YBCO/STO/YBCO multilayer with T c ( zero ) above 85 K for both YBCO micro-bridges of 50 μm width by depositing the insulating STO layer progressively at T s = 550°C and 780°C. The resistivity of both YBCO layers at room temperature is below 1.0 mΩ.cm.

Effect of columnar defects on the second magnetization peak in Bi2Sr2CaCu2O8 single crystals

Abstract The magnetic hysteresis loops and the relaxation in Bi 2 Sr 2 CaCu 2 O 8 single crystals of various doses of columnar defects (CDs) are studied mainly focusing on physical nature of anomalous second magnetization peak (SMP). With increasing CD density up to a matching field of 100 G, it is observed that the magnetization around the second peak systematically decreases, while the magnetization around the neck region between two peaks increases. The reduction of the SMP after introducing low-density CD is interpreted as CDs role of suppressing the decoupling transition of neighboring pancake vortices, thus resulting in a less enhanced magnetization compared to that of the unirradiated crystal. Both magnetization loops and the dynamic behavior of vortices seem to change near SMP suggesting a transition of vortex structure in that field region. We also observed that the experimental time window is an important factor for ability to observe the SMP. The experimental results are discussed in terms of both static and dynamic effects.

Synthesis and characterization of the infinite-layer superconductor Sr0.9La0.1CuO2☆

Abstract We report the high-pressure synthesis of the electron-doped infinite-layer superconductor Sr0.9La0.1CuO2. A Rietveld analysis using X-ray powder diffraction data showed that, within the resolution of the measurement, the sample was purely an infinite-layer structure without any discernible impurities. The superconducting volume fraction and the transition width were greatly improved compared to those in the previous reports. Also the irreversibility field line was much higher than that of (La,Sr)2CuO4. The higher value seems to originate from the strong interlayer coupling due to the reduced average distance between the CuO2 planes.

Oxygen states on the CuO chain of YBa2−xSrxCu3Oy

We have measured the weight change of YBa 2-x Sr x Cu 3 O y (0 ≤ x ≤ 1.0) samples with heating each up to 950°C at a rate of 2°C/min. in Ar. For pure YBa 2 Cu 3 O y , there is a maximum around 480°C in the curve of temperature derivative of weight, whereas, another maximum was observed around 630°C for Sr-substituted ones. As-sintered samples show sharp superconducting transition. After annealing in Ar atmosphere, however, Sr-substituted samples show two-step superconducting transitions while the transition width of pure YBa 2 Cu 3 O y remains relatively sharp. These results suggest that there are two states of oxygen on the Cu-O chain of the Sr-substituted samples. One is the same as that for the pure YBa 2 Cu 3 O y , and the other is more tightly bound state around the Sr ions due to the local contraction of the structure. The concentration of the latter increases as the Sr concentration increases.

Iodine intercalation effect on the critical fluctuation of Bi2Sr2CaCu2O8 single crystal

Abstract The magnetization of iodine intercalated Bi 2 Sr 2 CaCu 2 O 8 (I + Bi-2212) single crystal has been measured as a function of magnetic field H and temperature T. The extracted fluctuation part of the magnetization exhibits a critical behavior consistent with the three dimensional XY model. The static critical exponent ν is 0.99 ± 0.1, which is increased from the value 0.77 ± 0.1 for pristine Bi-2212, indicating that the weak interlayer coupling along the c-axis of iodine intercalated Bi-2212 significantly increases the static critical exponent ν. This result supports that Bi-2212 has an increased static critical exponent ν that is larger than the value of 0.669 of YBa 2 Cu 3 0 7−δ (YBCO) single crystal.

Critical dynamics of superconducting Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ single crystal

The magnetization and resistivity of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ (Bi-2212) single crystals have been measured as a function of magnetic field H and temperature T. The extracted fluctuation part of the magnetization and conductivity exhibit critical behavior consistent with the three dimensional XY model. The dynamic critical exponent z is 1.6/spl plusmn/0.1, which is close to the value for YBCO. The static critical exponent v is 0.769 and 0.909 respectively for the magnetization and conductivity data. The values of v are larger than that of YBCO. The results indicate that the weak interlayer coupling along the c-axis of Bi-2212 does not influence the dynamic critical exponent z but significantly increases the static critical exponent v.

Enhancement of vortex fluctuation in Bi2Sr2CaCu2O8 single crystal by iodine intercalation

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. Vortex fluctuation effects in pristine and iodine-intercalated Bi 2 Sr 2 CaCu 2 O 8 single crystals were studied in magnetic fields of 1 T ≤ H ≤ 5 T parallel to the c-axis. We found that iodine-intercalated specimen showed strong positional fluctuations of the vortices even far below the transition temperature due to the reduction of the interlayer coupling. Also. we obtaind various thermodynamic parameters (H r (0), H r2 (0), λ ab (0), and ξ ab (0)) using thc Hao-Clem and other related models.

Effects of Sr substitution on Tc of Y0.85Ca0.15Ba2−xSrxCu3Oy

Abstract We have studied the Ar annealing effect on T c of Y 0.85 Ca 0.15 Ba 2−x Cu 3 O y (x = 0.0, 0.5 and 1.0) samples, Ar annealing was carried out at 480°C for 15 min ∼ 10 h. As the annealing time increases, T c of the x = 0.0 and 0.5 samples first gradually increases to a maximum value, then it decreases slowly suggesting the assintered samples are in the over-doped state. However, the x = 1.0 sample shows an anomalous behavior. T c increases from 68 K to 75 K after Ar annealing for 15 ∼ 30 min, then it abruptly decreases to 40∼50 K after further Ar annealing.

Hall Effects in Bi2Sr2CaCu2−xNixO8+δ Single Crystals in Normal and Mixed States

We report the a-axis resistivity ρa(T) and Hall coefficient RH(T) measurements on Bi2Sr2CaCu2−xNixO8+δ (x=0.0, 0.02, 0.04) single crystals. The superconducting transition temperature decreases with increasing x. RH in the normal state is dependent on 1/T and in the mixed state the sign reversal of RH is observed for all samples. The impurity effects on the sign reversal of RH in the mixed state are discussed.