Josephson Vortex States in Intermediate Fields

Motivated by recent resistance data in high $T_c$ superconductors in fields {\it parallel} to the CuO layers, we address two issues on the Josephson-vortex phase diagram, the appearances of structural transitions on the observed first order transition (FOT) curve in intermediate fields and of a lower critical point of the FOT line. It is found that some rotated pinned solids are more stable than the ordinary rhombic pinned solids with vacant interlayer spacings and that, due to the vertical portion in higher fields of the FOT line, the FOT tends to be destroyed by creating a lower critical point.Comment: 12 pages, 3 figures. To appear in J.Phys.Soc.Jpn. 71, No.2 (February, 2002

Universal Irreversibility of Normal Quantum Diffusion

Time-reversibility measured by the deviation of the perturbed time-reversed motion from the unperturbed one is examined for normal quantum diffusion exhibited by four classes of quantum maps with contrastive physical nature. Irrespective of the systems, there exist a universal minimal quantum threshold above which the system completely loses the past memory, and the time-reversed dynamics as well as the time-reversal characteristics asymptotically trace universal curves independent of the details of the systems.Comment: 4 pages, 4 figure

Evidence for realignment of the charge density wave state in ErTe3_3 and TmTe3_3 under uniaxial stress via elastocaloric and elastoresistivity measurements

We report the evolution of a charge density wave (CDW) state in the quasi-2D rare-earth tritellurides ($R$Te$_3$ for $R$=Er,Tm) as a function of in-plane uniaxial stress. Measurements of the elastocaloric effect, resistivity, and elastoresistivity allow us to demonstrate the importance of in-plane antisymmetric strain on the CDW and to establish a phase diagram. We show that modest tensile stress parallel to the in-plane $a$-axis can reversibly switch the direction of the ordering wavevector between the two in-plane directions. This work establishes $R$Te$_3$ as a promising model system for the study of strain-CDW interactions in a quasi-2D square lattice.Comment: 18 pages, 12 figure

Uniaxial-Pressure induced Ferromagnetism of Enhanced Paramagnetic Sr3Ru2O7

We report a uniaxial pressure-dependence of magnetism in layered perovskite strontium ruthenate Sr3Ru2O7. By applying a relatively small uniaxial pressure, greater than 0.1 GPa normal to the RuO2 layer, ferromagnetic ordering manifests below 80 K from the enhanced-paramagnet. Magnetization at 1 kOe and 2 K becomes 100 times larger than that under ambient condition. Uniaxial pressure dependence of Curie temperature T_C suggests the first order magnetic transition. Origin of this uniaxial-pressure induced ferromagnetism is discussed in terms of the rotation of RuO6 octahedra within the RuO2 plane.Comment: 8 pages, 3 figures. to be published in Journal of the Physical Society of Japan, vol.73, No.5 (2004

Orbital selectivity of the kink in the dispersion of Sr2RuO4

We present detailed energy dispersions near the Fermi level on the monolayer perovskite ruthenate Sr2RuO4, determined by high-resolution angle-resolved photoemission spectroscopy. An orbital selectivity of the kink in the dispersion of Sr2RuO4 has been found: A kink for the Ru 4d_xy orbital is clearly observed, but not for the Ru 4d_yz and 4d_zx ones. The result provides insight into the origin of the kink.Comment: 5 pages, 4 figures. Accepted for publication in Phys. Rev.

Spin-charge-lattice coupling near the metal-insulator transition in Ca3Ru2O7

We report x-ray scattering studies of the c-axis lattice parameter in Ca3Ru2O7 as a function of temperature and magnetic field. These structural studies complement published transport and magnetization data, and therefore elucidate the spin-charge-lattice coupling near the metal-insulator transition. Strong anisotropy of the structural change for field applied along orthogonal in-plane directions is observed. Competition between a spin-polarized phase that does not couple to the lattice, and an antiferromagnetic metallic phase, which does, gives rise to rich behavior for B $\parallel$ b.Comment: 6 pages, 4 figures, to appear in Phys. Rev.

Molecular-orbital structure in neutron-rich C isotopes

The molecule-like structure of the C isotopes (A=12, 14, 16) is investigated using a microscopic $\alpha+\alpha+\alpha+n+n+\cdot \cdot \cdot$ model. The valence neutrons are classified based on the molecular-orbit (MO) model, and both $\pi$-orbit and $\sigma$-orbit are introduced around three $\alpha$-clusters. The valence neutrons which occupy the $\pi$-orbit increase the binding energy and stabilize the linear-chain of 3$\alpha$ against the breathing-like break-up. However, $^{14}$C with the $\pi$-orbit does not show clear energy minimum against the bending-like path. The combination of the valence neutrons in the $\pi$- and the $\sigma$-orbit is promising to stabilize the linear-chain state against the breathing- and bending- modes, and it is found that the excited states of $^{16}$C with the $(3/2^-_\pi)^2(1/2^-_\sigma)^2$ configuration for the four valence neutrons is one of the most promising candidates for such structure

Theoretical Description of Resistive Behavior near a Quantum Vortex-Glass Transition

Resistive behaviors at nonzero temperatures (T > 0) reflecting a quantum vortex-glass (VG) transition (the so-called field-tuned superconductor-insulator transition at T=0) are studied based on a quantum Ginzburg-Landau (GL) action for a s-wave pairing case containing microscopic details. The ordinary dissipative dynamics of the pair-field is assumed on the basis of a consistency between the fluctuation conductance terms excluded from GL approach and an observed negative magnetoresistance. It is shown that the VG contribution, G_{vg}(B=B_{vg}, T \to 0),to 2D fluctuation conductance at the VG transition field B_{vg} depends on the strength of a repulsive-interaction between electrons and takes a universal value only in the ordinary dirty limit neglecting the electron-repulsion. Available resistivity data near B_{vg} are discussed based on our results, and extensions to the cases of a d-wave pairing and of 3D systems are briefly commented on.Comment: Explanation of data in strongly disordered case, as well as Fig.2 and 3, was renewed, and comments on recent publications were added. To appear in J.Phys.Soc. Jp

Metamagnetism and critical fluctuations in high quality single crystals of the bilayer ruthenate Sr3Ru2O7

We report the results of low temperature transport, specific heat and magnetisation measurements on high quality single crystals of the bilayer perovskite Sr3Ru2O7, which is a close relative of the unconventional superconductor Sr2RuO4. Metamagnetism is observed, and transport and thermodynamic evidence for associated critical fluctuations is presented. These relatively unusual fluctuations might be pictured as variations in the Fermi surface topography itself. No equivalent behaviour has been observed in the metallic state of Sr2RuO4.Comment: 4 pages, 4 figures, Revtex 3.

Heterogeneity Induced Order in Globally Coupled Chaotic Systems

Collective behavior is studied in globally coupled maps with distributed nonlinearity. It is shown that the heterogeneity enhances regularity in the collective dynamics. Low-dimensional quasiperiodic motion is often found for the mean-field, even if each element shows chaotic dynamics. The mechanism of this order is due to the formation of an internal bifurcation structure, and the self-consistent dynamics between the structures and the mean-field. Keywords: Globally Coupled Map with heterogeneity, Collective behaviorComment: 11 pages (Revtex) + 4 figures (PostScript,tar+gzip