1,610 research outputs found
A generalization of the Artin-Tate formula for fourfolds
We give a new formula for the special value at s=2 of the Hasse-Weil zeta
function for smooth projective fourfolds under some assumptions (the Tate and
Beilinson conjecture, finiteness of some cohomology groups, etc.). Our formula
may be considered as a generalization of the Artin-Tate(-Milne) formula for
smooth surfaces, and expresses the special zeta value almost exclusively in
terms of inner geometric invariants such as higher Chow groups (motivic
cohomology groups). Moreover we compare our formula with Geisser's formula for
the same zeta value in terms of Weil-\'etale motivic cohomology groups, and as
a consequence (under additional assumptions) we obtain some presentations of
weight two Weil-\'etale motivic cohomology groups in terms of higher Chow
groups and unramified cohomology groups.Comment: 18 page
The band-gap structures and recovery rules of generalized n-component Fibonacci piezoelectric superlattices
The spectral evolution from periodic structure to random structure has always
been an interesting topic in solid state physics, the generalized n-component
Fibonacci sequences (n- CF) provide a convenient tool to investigate such
process since its randomness can be controlled via the parameter n. In this
letter, the band-gap structures of n-CF piezoelectric superlattices have been
calculated using the transfer-matrix-method, the self-similarity behavior and
recovery rule have been systematically analyzed. Consistent with the rigorous
mathematical proof by Hu et al.[A. Hu et al. Phys. Rev. B. 48, 829 (1993)], we
find that the n-CF sequences with 2 \leq n \leq 4 are identified as
quasiperiodic. The imaginary wave numbers are characterized by the self-similar
spectrum, their major peaks can all be properly indexed. In addition, we find
that the n = 5 sequence belongs to a critical case which lies at the border
between quasiperiodic to aperiodic structures. The frequency range of
self-similarity pattern approaches to zero and a unique indexing of imaginary
wave numbers becomes impossible. Our study offers the information on the
critical 5-CF superlattice which was not available before. The classification
of band-gap structures and the scaling laws around fixed points are also given
Zero modes and the edge states of the honeycomb lattice
The honeycomb lattice in the cylinder geometry with zigzag edges, bearded
edges, zigzag and bearded edges (zigzag-bearded), and armchair edges are
studied. The tight-binding model with nearest-neighbor hoppings is used. Edge
states are obtained analytically for these edges except the armchair edges. It
is shown, however, that edge states for the armchair edges exist when the the
system is anisotropic. These states have not been known previously. We also
find strictly localized states, uniformly extended states and states with
macroscopic degeneracy.Comment: 6 pages 8 figure
Correlations in one-dimensional disordered electronic systems with interaction
We investigate the effects of randomness in a strongly correlated electron
model in one-dimension at half-filling. The ground state correlation functions
are exactly written by products of 33 transfer matrices and are
evaluated numerically. The correlation lengths depend on randomness when the
interaction is effectively weak. On the contrary, they are completely
insensitive to randomness when the interaction is effectively strong.Comment: 7 pages, Revte
Localization problem of the quasiperiodic system with the spin orbit interaction
We study one dimensional quasiperiodic system obtained from the tight-binding
model on the square lattice in a uniform magnetic field with the spin orbit
interaction. The phase diagram with respect to the Harper coupling and the
Rashba coupling are proposed from a number of numerical studies including a
multifractal analysis. There are four phases, I, II, III, and IV in this order
from weak to strong Harper coupling. In the weak coupling phase I all the wave
functions are extended, in the intermediate coupling phases II and III mobility
edges exist, and accordingly both localized and extended wave functions exist,
and in the strong Harper coupling phase IV all the wave functions are
localized. Phase I and Phase IV are related by the duality, and phases II and
III are related by the duality, as well. A localized wave function is related
to an extended wave function by the duality, and vice versa. The boundary
between phases II and III is the self-dual line on which all the wave functions
are critical. In the present model the duality does not lead to pure spectra in
contrast to the case of Harper equation.Comment: 10 pages, 11 figure
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