Magnetic-field effects on the in-plane electrical resistivity in the single-crystal La2−x_{2-x}Bax_xCuO4_4 and La1.6−x_{1.6-x}Nd0.4_{0.4}Srx_xCuO4_4 around x=1/8x=1/8: Relating to the field-induced stripe order

Temperature dependence of the in-plane electrical resistivity, $\rho_{\rm ab}$, in various magnetic fields has been measured in the single-crystal La$_{2-x}$Ba$_x$CuO$_4$ with $x=0.08$, 0.10, 0.11 and La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ with $x=0.12$. It has been found that the superconducting transition curve shows a so-called fan-shape broadening in magnetic fields for $x=0.08$, while it shifts toward the low-temperature side in parallel with increasing field for $x=0.11$ and 0.12 where the charge-spin stripe order is formed at low temperatures. As for $x=0.10$, the broadening is observed in low fields and it changes to the parallel shift in high fields above 9 T. Moreover, the normal-state value of $\rho_{\rm ab}$ at low temperatures markedly increases with increasing field up to 15 T. It is possible that these pronounced features of $x=0.10$ are understood in terms of the magnetic-field-induced stabilization of the stripe order suggested from the neutron-scattering measurements in the La-214 system. The $\rho_{\rm ab}$ in the normal state at low temperatures has been found to be proportional to ln(1/$T$) for $x=0.10$, 0.11 and 0.12. The ln(1/$T$) dependence of $\rho_{\rm ab}$ is robust even in the stripe-ordered state.Comment: 6 pages, 4 figures, ver. 2 has been accepted for publication in Phys. Rev.

Search for long-lived massive particles in extensive air showers

Air showers containing delayed sub-showers which may be produced by a long-lived massive particle have been investigated by using twelve detectors. Ten events have been selected out as the candidates. However, a definite conclusion cannot be reached at the present time

Wilson ratio of a Tomonaga-Luttinger liquid in a spin-1/2 Heisenberg ladder

Using micromechanical force magnetometry, we have measured the magnetization of the strong-leg spin-1/2 ladder compound (C$_7$H$_{10}$N)$_2$CuBr$_2$ at temperatures down to 45 mK. Low-temperature magnetic susceptibility as a function of field exhibits a maximum near the critical field H_c at which the magnon gap vanishes, as expected for a gapped one-dimensional antiferromagnet. Above H_c a clear minimum appears in the magnetization as a function of temperature as predicted by theory. In this field region, the susceptibility in conjunction with our specific heat data yields the Wilson ratio R_W. The result supports the relation R_W=4K, where K is the Tomonaga-Luttinger-liquid parameter

Synthesis of infinite-layer LaNiO2 films by metal-organic deposition

We report the synthesis of infinite-layer LaNiO2 thin films by metal organic decomposition. Our work is aimed to synthesize perovskite-like oxides with 3d9 electronic configuration, which is common to high-Tc copper oxides. The 3d9 configuration is very rare in oxides other than cuprates. Ni1+ oxides, even though Ni1+ is an unusual oxidation state, may be one of very few candidates. One example of the Ni1+ phases is infinite-layer LaNiO2. The bulk synthesis of LaNiO2 is difficult, but we demonstrate in this article that the thin-film synthesis of LaNiO2 by metal organic decomposition is rather easy. This is due to the advantage of thin films with a large-surface-to-volume ratio, which makes oxygen diffusion prompt. Resistivity measurements indicate that LaNiO2 is essentially a metal but unfortunately with no trace of superconductivity yet.Comment: 13 pages, 4 figure

Generic phase diagram of "electron-doped" T' cuprates

We investigated the generic phase diagram of the electron doped superconductor, Nd2-xCexCuO4, using films prepared by metal organic decomposition. After careful oxygen reduction treatment to remove interstitial Oap atoms, we found that the Tc increases monotonically from 24 K to 29 K with decreasing x from 0.15 to 0.00, demonstrating a quite different phase diagram from the previous bulk one. The implication of our results is discussed on the basis of tremendous influence of Oap "impurities" on superconductivity and also magnetism in T' cuprates. Then we conclude that our result represents the generic phase diagram for oxygen-stoichiometric Nd2-xCexCuO4.Comment: 12 pages, 4 figures; International Symposium on Superconductivity (ISS) 200

Neutron Scattering Study of Temperature-Concentration Phase Diagram of (Cu1-xMgx)GeO3

In doped CuGeO3 systems, such as (Cu1-xZnx)GeO3 and Cu(Ge1-xSix)O3, the spin-Peierls (SP) ordering (T<Tsp) coexists with the antiferromagnetic (AF) phase (T<TN<Tsp). Tsp decreases while TN increases with increasing x in low doping region. For higher x, however, the SP state disappears and only the AF state remains. These features are common for all the doped CuGeO3 systems so far studied, indicating the existence of universal T-x phase diagram. Recently, Masuda et al. carried out comprehensive magnetic susceptibility (chi) measurements of (Cu1-xMgx)GeO3, in which doping concentration can be controlled significantly better than the Zn doped systems. They found that TN suddenly jumps from 3.43 to 3.98K at the critical concentration xc sim 0.023 and that a drop in chi corresponding to the SP ordering also disappears at x>xc. They thus concluded that there is a compositional phase boundary between two distinct magnetic phases. To clarify the nature of two phases, we performed neutron-scattering measurements on (Cu1-xMgx)GeO3 single crystals with various x. Analysis of the data at fixed temperature points as a function of doping concentration has revealed sudden changes of order parameters at the critical concentration xc=0.027 +- 0.001. At finite temperatures below TN, the drastic increase of the AF moment takes place at xc. The spin-Peierls order parameter delta associated with lattice dimerization shows a precipitous decrease at all temperature below Tsp. However, it goes to zero above xc only at the low temperature limit.Comment: 9 pages, 9 figure