arXiv subjects

A. Iyo

Publications and source records attributed to A. Iyo.

93 records · Page 6Linked to original sources

arXiv2002

Paramagnetic Meissner Effect in Superconducting Single Crystals of Ba_{1-x}K_xBiO_3

The paramagnetic Meissner effect (PME) in the field cooled susceptibility has been observed in superconducting single crystals of Ba_{1-x}K_xBiO_3 using magnetometers of Quantum-Design Co.. The PME is similar to that observed in cuprates and Nb superconductors. For the Ba_{0.63}K_{0.37}BiO_3 crystal, the PME is observed in cooling process under the field up to 750 Oe. The PME was not found in the virgin-charged superconducting magnet. The PME is found in a superconductor with trapped flux and may arise from a remnant field, a temperature inhomogeneity near T_c, and a potassium-concentration inhomogeneity.

cond-mat.supr-con↗

arXiv2001

EXAFS study of Tl$_{0.75}$Cu$_{.25}$Ba$_2$Ca$_3$Cu$_4$ O$_y$ and Cu$_{0.68}$C$_{.32}$Ba$_2$Ca$_3$Cu$_4$ O$_y$ superconductors [bulk] at 300 K

The results of EXAFS measurements at 300 K for the superconducting compounds Tl$_{0.75}$Cu$_{0.25}$Ba$_{2}$Ca$_{3}$Cu$_4$O$_{y}$ [Tl-1234], TlBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{y}$ [Tl-1212], and CuBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{y}$ [Cu-1234]. are reported. We have measured the EXAFS spectrum for Tl$_{0.75}$Cu$_{0.25}$Ba$_{2}$Ca$_{3}$Cu$_4$O$_{y}$ in the range 10K-300K, however here we limit our discussion to the spectrum at 300 K. This material is prepared under high pressure [3.5 GPa] from precursors with small carbon concentrations and exhibits a T$_c$ of $~127$ K. We have also performed ``aging'' study by looking at XRD for this material after approximately one year. The XRD results at 300 K are ``unchanged''. It is of interest to compare the EXAFS spectrum of this compound with the corresponding compound Cu-1234. Remarks on the choice of appropriate EXAFS standard for this and related compounds are also given. Based on our data analysis we quantify disorder in these systems. By using the Cu-O in-plane distance we give values for the microstrain parameter, which can be related to the charge ordering transition.

cond-mat.supr-con↗

arXiv2000

Two-Dimensional Nature of Four-Layer Superconductors by Inequivalent Hole Distribution

The magnetization of the four-layer superconductor CuBa_{2}Ca_{3}Cu_4O_{12-δ} with T_c\simeq117 K is presented. The high-field magnetization around T_c(H) follows the exact two-dimensional scaling function given by Tešanović and Andreev. This feature is contrary to the inference that the interlayer coupling becomes strong if the number of CuO_2 planes in a unit cell increases. Also, the fluctuation-induced susceptibility in the low-field region was analyzed by using the modified Lawrence-Doniach model. The effective number of independently fluctuating CuO_2 layers per unit cell, g_{\rm eff}, turned out to be \simeq 2 rather than 4, which indicated that two among the four CuO_2 layers were in states far from their optimal doping levels. This result could explain why CuBa_{2}Ca_{3}Cu_4O_{12-δ} shows two-dimensional behavior.

cond-mat.supr-con↗