41,029 research outputs found
Mott transition and heavy fermion state in the pyrochlore Hubbard model
We investigate the interplay between geometrical frustration and strong
electron correlation based upon the pyrochlore Hubbard model. In the
half-filling case, using the perturbative expansion in terms of electron
correlation, we show that the self-energy shows a divergent behavior leading
the system into the Mott insulating state, in which quantum disordered spin
liquid without magnetic long-range order realizes. In the hole-doped case, we
obtain heavy-fermion-like Fermi liquid state. We also calculate the neutron
cross section which is well consistent with recent neutron scattering
experiments for itinerant pyrochlore systems.Comment: 5 pages, 5 figures, revised version accepted for the publication in
Phys. Rev.
When does "Time" become "Observable" ?
We investigate some spectral properties of time operators which are obtained
through Canonical Commutation Relation (CCR) and Positive Operator Valued
Measure (POVM) of quantum physics. In addition, we re-interpret the spectral
properties of time operators from the standpoint of the Copenhagen
Interpretation, especially, of W.Heisenberg.Comment: 9 pages, The Ryukoku Journal of Humanities and Science, Vol.35 No.2,
March, 201
Metal-to-Insulator Transition, Spin Gap Generation, and Charge Ordering in Geometrically Frustrated Electron Systems
We investigate a (semi-)metal to insulator transition (MIT) realized in
geometrically frustrated electron systems on the basis of the Hubbard model on
a three-dimensional pyrochlore lattice and a two-dimensional checkerboard
lattice. Using the renormalization group method and mean field analysis, we
show that in the half-filling case, MIT occurs as a result of the interplay
between geometrical frustration and electron correlation. In the insulating
phase, which has a spin gap, the spin rotational symmetry is not broken, while
charge ordering exists. The charge ordered state is stabilized so as to relax
the geometrical frustration in the spin degrees of freedom. We also discuss the
distortion of the lattice structure caused by the charge ordering. The results
are successfully applied to the description of the MIT observed in the
pyrochlore system .Comment: 12 pages, 10 figure
Stable photosensor amplifiers
Minimization of common mode effects in differential amplifier arrangement which processes signals from two high impedance photosensors is achieved by connecting one photosensor in feedback loop of amplifier and using field effect transistors in the input circuit
Pseudogap Phenomena in the BCS Pairing Model
We investigate pseudo-gap phenomena realized in the BCS pairing model with a
long but finite interaction range. We calculate the single-particle self-energy
in all order exactly in the temperature range where the superconducting
fluctuation propagator is Gaussian-like. It is found that vertex corrections to
the self-energy which are discarded in the previous studies are crucially
important for the pseudo-gap of the single-particle density of states in higher
order calculations.Comment: 7 pages, 3 figures, references are added, to appear in J. Phys. Soc.
Jpn. vol.71, no.5 (2002
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