19,637 research outputs found
A sensitive cloud chamber without radioactive sources
We present a sensitive diffusion cloud chamber which does not require any
radioactive sources. A major difference from a commonly used chamber is use of
a heat sink as its bottom plate. A result of a performance test of the chamber
is given.Comment: 8 pages, 8 figures, iopart.cls, figures and references adde
Novel Charge Order and Superconductivity in Two-Dimensional Frustrated Lattice at Quarter Filling
Motivated by the various physical properties observed in
-(BEDT-TTF)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
-wave superconductivity. We discuss the relation to the real materials and
propose the unified view of the family of -(BEDT-TTF)X.Comment: 4 pages, 5 figure
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
Charge ordering in theta-(BEDT-TTF)_2 X materials
We investigate theoretically charge ordered states on the anisotropic
triangular lattice characteristic of the theta-(BEDT-TTF)_2 X materials. Using
exact diagonalization studies, we establish that the charge order (CO) pattern
corresponds to a ``horizontal'' stripe structure, with ...1100... CO along the
two directions with larger electron hopping (p-directions), and ...1010... CO
along the third direction (c-direction). The CO is accompanied by co-operative
bond dimerizations along all three directions in the highest spin state. In the
lowest spin state bonds along the p-directions are tetramerized. Our theory
explains the occurence of a charge-induced high temperature transition as well
as a spin gap transition at lower temperature.Comment: 4 pages, 4 eps figures, uses jpsj2.cl
Quantum Melting of Charge Order due to Frustration in Two-Dimensional Quarter-Filled Systems
The effect of geometrical frustration in a two-dimensional 1/4-filled
strongly correlated electron system is studied theoretically, motivated by
layered organic molecular crystals. An extended Hubbard model on the square
lattice is considered, with competing nearest neighbor Coulomb interaction, V,
and that of next-nearest neighbor along one of the diagonals, V', which favor
different charge ordered states. Based on exact diagonalization calculations,
we find a metallic phase stabilized over a broad window at V' ~ V even for
large Coulomb repulsion strengths as a result of frustrating the charge ordered
states. Slightly modifying the lattice geometry relevant to the actual organic
compounds does not alter the results, suggesting that this `quantum melting' of
charge order is a robust feature of frustrated strongly correlated 1/4-filled
systems.Comment: 5 pages, 4 figures, to be published in Phys. Rev.
2-elementary subgroups of the space Cremona group
We give a sharp bound for orders of elementary abelian 2-groups of birational
automorphisms of rationally connected threefolds
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