Intermediate phase of the one dimensional half-filled Hubbard-Holstein model

We present a detailed numerical study of the Hubbard-Holstein model in one dimension at half filling, including full finite-frequency quantum phonons. At half filling, the effects of the electron-phonon and electron-electron interactions compete, with the Holstein phonon coupling acting as an effective negative Hubbard onsite interaction U that promotes on-site electron pairs and a Peierls charge-density wave state. Most previous work on this model has assumed that only Peierls or U>0 Mott insulator phases are possible at half filling. However, there has been speculation that a third metallic phase exists between the Peierls and Mott phases. We present results confirming the intermediate metallic phase, and show that the Luttinger liquid correlation exponent K_rho>1 in this region, indicating dominant superconducting pair correlations. We explore the full phase diagram as a function of onsite Hubbard U, phonon coupling constant, and phonon frequency.Comment: 4 pages, 4 EPS figures. v2: typos corrected. To appear in Phys. Rev. Let

Three-dimensional boundary layer analysis program Blay and its application

The boundary layer calculation program (BLAY) is a program code which accurately analyzes the three-dimensional boundary layer of a wing with an undefined plane. In comparison with other preexisting programs, the BLAY is characterized by the following: (1) the time required for computation is shorter than any other; (2) the program is adaptable to a parallel processing computer; and (3) the program is associated with a secondary accuracy in the z-direction. As a boundary layer modification to transonic nonviscous flow analysis programs, it is used to adjust viscous and nonviscous interference problems repeatedly. Its efficiency is an important factor in cost reduction in aircraft designing

Asynchronous vibration problem of centrifugal compressor

An unstable asynchronous vibration problem in a high pressure centrifugal compressor and the remedial actions against it are described. Asynchronous vibration of the compressor took place when the discharge pressure (Pd) was increased, after the rotor was already at full speed. The typical spectral data of the shaft vibration indicate that as the pressure Pd increases, pre-unstable vibration appears and becomes larger, and large unstable asynchronous vibration occurs suddenly (Pd = 5.49MPa). A computer program was used which calculated the logarithmic decrement and the damped natural frequency of the rotor bearing systems. The analysis of the log-decrement is concluded to be effective in preventing unstable vibration in both the design stage and remedial actions

Ab initio derivation of electronic low-energy models for C60 and aromatic compounds

We present a systematic study for understanding the relation between electronic correlation and superconductivity in C60 and aromatic compounds. We derived, from first principles, extended Hubbard models for twelve compounds; fcc K3C60, Rb3C60, Cs3C60 (with three different lattice constants), A15 Cs3C60 (with four different lattice constants), doped solid picene, coronene, and phenanthrene. We show that these compounds are strongly correlated and have a similar energy scale of the bandwidth and interaction parameters. However, they have a different trend in the relation between the strength of electronic correlation and superconducting transition temperature; while the C60 compounds have a positive correlation, the aromatic compounds exhibit negative correlation.Comment: 13 pages, 7 figures, 7 table

Unconventional metallic conduction in two-dimensional Hubbard-Wigner lattices

The interplay between long-range and local Coulomb repulsion in strongly interacting electron systems is explored through a two-dimensional Hubbard-Wigner model. An unconventional metallic state is found in which collective low-energy excitations characteristic of the Wigner crystal induce a flow of electrical current despite the absence of one-electron spectral weight at the Fermi surface. Photoemission experiments on certain quarter-filled layered molecular crystals should observe a gap in the excitation spectrum whereas optical spectroscopy should find a finite Drude weight indicating metallic behavior.Comment: 10 pages, accepted for publication in PR

Absence of superconductivity in the half-filled band Hubbard model on the anisotropic triangular lattice

We report exact calculations of magnetic and superconducting pair-pair correlations for the half-filled band Hubbard model on an anisotropic triangular lattice. Our results for the magnetic phases are similar to those obtained with other techniques. The superconducting pair-pair correlations at distances beyond nearest neighbor decrease monotonically with increasing Hubbard interaction U for all anisotropy, indicating the absence of frustration-driven superconductivity within the model.Comment: 4 pages, 4 EPS figure

Coexistence of Spin Density Wave and Triplet Superconductivity

We discuss the possibility of coexistence of spin density wave (antiferromagnetism) and triplet superconductivity as a particular example of a broad class of systems where the interplay of magnetism and superconductivity is important. We focus on the case of quasi-one-dimensional metals, where it is known experimentally that antiferromagnetism is in close proximity to triplet superconductivity in the temperature versus pressure phase diagram. Over a narrow range of pressures, we propose an intermediate non-uniform phase consisting of alternating antiferromagnetic and triplet superconducting stripes. Within the non-uniform phase there are also changes between two and three dimensional behavior.Comment: Revtex4, 4 pages, 5 figure

Dark filaments observed at 8.3mm and 3.1mm wavelength

Mapping of the sun was made at 3.1mm (98 GHz) and 8.3mm (36 GHz) wavelengths with a 45m dish radio telescope at the Nobeyama Cosmic Radio Observatory. The depressions associated with large H alpha filaments are derived to be -0.2 at 8.3mm and -0.05 at 3.1mm, which are darker than the values inferred by Raoult et al. (1979

Charge ordering in \theta-(BEDT-TTF)2RbZn(SCN)4: Cooperative effects of electron correlations and lattice distortions

Combined effects of electron correlations and lattice distortions are investigated on the charge ordering in \theta-(BEDT-TTF)2RbZn(SCN)4 theoretically in a two-dimensional 3/4-filled extended Hubbard model with electron-lattice couplings. It is known that this material undergoes a phase transition from a high-symmetry metallic state to a low-symmetry insulating state with a horizontal-stripe charge order (CO) by lowering temperature. By means of the exact-diagonalization method, we show that electron-phonon interactions are crucial to stabilize the horizontal-stripe CO and to realize the low-symmetry crystal structure.Comment: 7 peges, 7 figures, accepted for publication in Phys. Rev.