Nonlinear Conduction by Melting of Stripe-Type Charge Order in Organic Conductors with Triangular Lattices

We theoretically discuss the mechanism for the peculiar nonlinear conduction in quasi-two-dimensional organic conductors \theta-(BEDT-TTF)2X [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] through the melting of stripe-type charge order. An extended Peierls-Hubbard model attached to metallic electrodes is investigated by a nonequilibrium Green's function technique. A novel current-voltage characteristic appears in a coexistent state of stripe-type and nonstripe 3-fold charge orders, where the applied bias melts mainly the stripe-type charge order through the reduction of lattice distortion, whereas the 3-fold charge order survives. These contrastive responses of the two different charge orders are consistent with the experimental observations.Comment: 5 pages, 4 figures, to appear in J. Phys. Soc. Jp

Uniform Mixing of High-Tc Superconductivity and Antiferromagnetism on a Single CuO2 Plane in Hg-based Five-layered Cuprate

We report a site selective Cu-NMR study on under-doped Hg-based five-layered high-$T_{\rm c}$ cuprate HgBa2Ca4Cu5Oy with a Tc=72 K. Antiferromagnetism (AF) has been found to take place at TN=290 K, exhibiting a large antiferromagnetic moment of 0.67-0.69uB at three inner planes (IP's). This value is comparable to the values reported for non-doped cuprates, suggesting that the IP may be in a nearly non-doped regime. Most surprisingly, the AF order is also detected with M(OP)=0.1uB even at two outer planes (OP's) that are responsible for the onset of superconductivity (SC). The high-Tc SC at Tc = 72 K can uniformly coexist on a microscopic level with the AF at OP's. This is the first microscopic evidence for the uniform mixed phase of AF and SC on a single CuO2 plane in a simple environment without any vortex lattice and/or stripe order.Comment: 4 pages, 4 figures. To be published in Phys.Rev.Let

Novel Charge Order and Superconductivity in Two-Dimensional Frustrated Lattice at Quarter Filling

Motivated by the various physical properties observed in $\theta$-(BEDT-TTF)$_2$X, we study the ground state of extended Hubbard model on two-dimensional anisotropic triangular lattice at 1/4-filling with variational Monte Carlo method. It is shown that the nearest-neighbor Coulomb interaction enhances the charge fluctuation and it induces the anomalous state such as charge-ordered metallic state and the triplet next-nearest-neighbor $f$-wave superconductivity. We discuss the relation to the real materials and propose the unified view of the family of $\theta$-(BEDT-TTF)$_2$X.Comment: 4 pages, 5 figure

Global Simulation of the Jovian Magnetosphere: Transitional Structure From the Io Plasma Disk to the Plasma Sheet

Jupiter has a strong magnetic field, and a huge magnetosphere is formed through the solar wind-Jupiter interaction. The generated magnetosphere–ionosphere system is reproduced based on the 9-component Magnetohydrodynamics (MHD) and the current conservation in the ionosphere. Assuming Io plasma emission rate 1.4 t/sec, this paper reproduces self-consistently global magnetic configuration, generations of the field-aligned current (FAC) and aurora, formation of the Io plasma disk at 8–20 RJ, plasma corotation, instability in the plasma disk, transition from the Io plasma disk to the plasma sheet at 20–150 RJ, and the plasmoid ejection. The rotating Io plasma in the disk forms instabilities that promotes radial diffusion. H+ is supplied from the ionosphere along high-latitude magnetic field lines and mixed with heavy ions around 15–20 RJ. Beyond 20 RJ, mixed plasma diffuses further outward by the centrifugal force that can exceed magnetic tension. In the ionosphere, the main oval occurs at 13.7°–15.5° colatitude. The Io disk is inner side of magnetic field lines traced from the low-latitude edge of the main oval. Along magnetic field lines, the main oval is mapped from the outer edge of the Io disk to the entire plasma sheet accompanying rotation delay. Due to the corotation limit, convection is accompanied by plasmoid ejection. Back reaction of plasmoid ejection affects even transport process in the Io disk. The downward FAC occurs in the polar cap showing variability. The region of externally driven Dungey convection seems quite narrow

The Origin of the Charge Ordering and Its Relevance to Superconductivity in θ\theta-(BEDT-TTF)2_2X: The Effect of the Fermi Surface Nesting and the Distant Electron-Electron Interactions

The origin of the charge ordering in organic compounds $\theta$-(BEDT-TTF)$_2 X$ ($X=MM'$(SCN)$_4$, $M=$Tl,Rb,Co, $M'=$Cs,Zn) is studied using an extended Hubbard model. Calculating the charge susceptibility within random phase approximation (RPA), we find that the $(3\times 3)\sim (3\times 4)$ charge ordering observed at relatively high temperatures can be considered as a consequence of a cooperation between the Fermi surface nesting, controlled by the hopping integral in the $c$ direction, and the electron-electron interactions, where the distant (next nearest neighbor) interactions that have not been taken into account in most of the previous studies play an important role.Mean field analysis at T=0 also supports the RPA results, and further shows that in the $3\times 3$ charge ordered state, some portions of the Fermi surface remain ungapped and are nested with a nesting vector close to the modulation wave vector of the horizontal stripe ordering observed at low temperatures in $X=MM'$(SCN)$_4$. We further study the possibility of superconductivity by taking into account the distant off-site repulsions and the band structure corresponding to $X=$I$_3$, in which superconductivity is experimentally observed. We find that there is a close competition between $d_{xy}$-wave-like singlet pairing and $p_{x+2y}$-wave-like triplet pairing due to a cooperation between the charge and the spin fluctuations. The present analysis provides a possible unified understanding of the experimental phase diagram of the $\theta$-(BEDT-TTF)$_2 X$ family, ranging from a charge ordered insulator to a superconductor.Comment: 13 pages, 18 figures (Figs.5,6,7,14,15,18 compressed using jpeg2ps

Practical Evaluation of Security for Quantum Key Distribution

Many papers proved the security of quantum key distribution (QKD) system, in the asymptotic framework. The degree of the security has not been discussed in the finite coding-length framework, sufficiently. However, to guarantee any implemented QKD system requires, it is needed to evaluate a protocol with a finite coding-length. For this purpose, we derive a tight upper bound of the eavesdropper's information. This bound is better than existing bounds. We also obtain the exponential rate of the eavesdropper's information. Further, we approximate our bound by using the normal distribution.Comment: The manuscript has been modfie