Ota, K., Hamada, K., Takemura, R., Ohmaki, M., Machi, T., Tanabe, K., ...
We investigated macroscopic quantum tunneling (MQT) of Bi$_2$Sr$_2$CaCu$_2$O$_y$ intrinsic Josephson junctions (IJJs) with two device structures. One is a nanometer-thick small mesa structure with...
Hg-Based Superconducting Cuprates: High Tc and Pseudo Spin-Gap (2008)
A brief review of microscopic studies of high-Tc superconductors HgBa2CuO4+d and HgBa2CaCu2O6+d is presented. The topics concerned are the pseudo spin-gap, the antiferromagnetic spin fluctuations...
Re-appearance of antiferromagnetic ordering with Zn and Ni substitution in La_{2-x}Sr_xCuO_4 (2003)
Machi, T., Kato, I., Hareyama, R., Watanabe, N., Itoh, Y., Koshizuka, N., ...
The effects of nonmagnetic Zn and magnetic Ni substitution for Cu site on magnetism are studied by measurements of uniform magnetic susceptibility for lightly doped La_{2-x}Sr_xCu_{1-z}M_zO_4 (M=Zn...
Zn-Neighbor Cu NQR in Zn-Substituted YBa2Cu3O7-d and YBa2Cu4O8 (2003)
Itoh, Y., Machi, T., Kasai, C., Adachi, S., Watanabe, N., Koshizuka, N., ...
We studied local electronic states near Zn in optimally doped YBa$_2$(Cu$_{1-x}$Zn_x)$_3$O$_{7-\delta}$ and underdoped YBa$_2$(Cu$_{1-x}$Zn_x)$_4$O$_8$ via satellite signals of plane-site Cu(2)...
Time evolution of superconducting properties of MgB2 exposed to water (2003)
Machi, T, Koshizuka, N, Murakami, M
The degradation of the superconducting properties, such as the diamagnetic magnetization (Mdia), the critical current density (Jc), and the irreversibility field (Hirr) for MgB2 exposed to water has...
Ti doping on the flux pinning and chemical stability against water of MgB2 bulk material (2003)
Feng, Y, Machi, T, Huang, D, Zhou, L, ...
Ti-doped MgB2 superconductors with different doping levels were prepared by solid-state reaction at ambient pressure. Jc of the samples changes with the doping level, with the best result achieved at...
Improvement of critical current density in MgB2 by Ti, Zr and Hf doping (2003)
Goto, D, Machi, T, Koshizuka, N, Murakami, M, Arai, S
Ti, Zr and Hf doped MgB2 polycrystalline samples have been prepared by using a hot pressing technique. In Ti doped MgB2, it was found that the optimum concentration of Ti for the critical current...
Ni-substituted sites and the effect on Cu electron spin dynamics of YBa2Cu{3-x}NixO{7-\delta} (2002)
Itoh, Y., Adachi, S., Machi, T., Ohashi, Y., Koshizuka, N.
We report Cu nuclear quadrupole resonance experiment on magnetic impurity Ni-substituted YBa$_2$Cu$_{3-x}$Ni$_x$O$_{7-\delta}$. The distribution of Ni-substituted sites and its effect on the Cu...
Enhancement of Critical Current Density in MgB2 Bulk Superconductors by Ti Doping (2002)
Feng, Y, Machi, T, Huang, D, Fudamoto, Y, ...
We studied the Ti doping effect on the superconducting properties and microstructure of sintered MgB2 bulk polycrystals. Using Ti as a sintering assistant, we have fabricated MgB2 bulk materials...
Improved Chemical Stability to Water in Ti-doped MgB2 (2002)
Machi, T, Koshizuka, N, Murakami, M
We investigated the degradation of critical current density (Jc) and irreversibility field (Hirr) of pure and Ti-doped MgB2 bulks by exposing the samples to water for a total of 10, 48, 100, and 124...
Nanoparticle structure of MgB2 with ultrathin TiB2 grain boundaries (2002)
Huang, D, Feng, Y, Machi, T, Koshizuka, N, ...
The microstructure of the Ti-doped MgB2 which shows a significantly improved critical current density, Jc [Appl. Phys. Lett. 79, 1154 (2001)], is investigated. It is found that Ti does not occupy the...
Zn-doping dependence of the wipeout region around Zn in YBa2(Cu1-xZnx)4O8 (2001)
Itoh, Y., Machi, T., Watanabe, N., Adachi, S., Kasai, C., Koshizuka, N.
We estimated the spread of the magnetically enhanced regions (wipeout regions) around Zn ions in high-Tc superconductors YBa2(Cu1-xZnx)4O8 (x=0, 0.005, 0.01, and 0.022) at T=4.2 K, via the planar...
Itoh, Y., Adachi, S., Machi, T., Koshizuka, N.
We report a zero-field Cu nuclear quadrupole resonance (NQR) study on the effects of nonmagnetic Sr substitution for high-Tc superconductors, Y(Ba1-xSrx)2Cu4O8 (Tc=82-80 K for x=0-0.4), using a...
Itoh, Y., Machi, T., Koshizuka, N., Masuda, T., Uchinokura, K.
We report on a zero-field 63Cu nuclear quadrupole resonance (NQR) study of nonmagnetic Mg impurity substituted Cu1-xMgxGeO3 (single crystals; the spin-Peierls transition temperature Tsp~14, 13.5, and...
Cu NQR study of host and guest spin dynamics in impurity-doped YBa2Cu4O8 (2001)
Itoh, Y., Machi, T., Watanabe, N., Koshizuka, N.
We present the planar 63Cu nuclear spin-lattice relaxation study of impurity-doped YBa2(Cu1-xMx)4O8 (M=Ni, Zn) at T=4.2-300 K with Cu nuclear quadrupole resonance (NQR) spin-echo technique. In the...
Spin Dynamics near the Superconductor-to-Insulator Transition in Impurity-Doped YBa2Cu4O8 (2001)
Itoh, Y., Machi, T., Watanabe, N., Adachi, S., Koshizuka, N.
We studied low-frequency spin dynamics near the impurity-induced superconductor-to-insulator transition for underdoped high-Tc superconductor YBa2(Cu1-xMx)4O8 (M=Ni, Zn) using the Cu nuclear...