12,218 research outputs found
Hall plateau diagram for the Hofstadter butterfly energy spectrum
We extensively study the localization and the quantum Hall effect in the
Hofstadter butterfly, which emerges in a two-dimensional electron system with a
weak two-dimensional periodic potential. We numerically calculate the Hall
conductivity and the localization length for finite systems with the disorder
in general magnetic fields, and estimate the energies of the extended levels in
an infinite system. We obtain the Hall plateau diagram on the whole region of
the Hofstadter butterfly, and propose a theory for the evolution of the plateau
structure with increasing disorder. There we show that a subband with the Hall
conductivity has separated bunches of extended levels, at least
for an integer . We also find that the clusters of the subbands with
identical Hall conductivity, which repeatedly appear in the Hofstadter
butterfly, have a similar localization property.Comment: 9 pages, 12 figure
Megaton Water Cerenkov Detectors and Astrophysical Neutrinos
Although formal proposals have not yet been made, the UNO and
Hyper-Kamiokande projects are being developed to follow-up the tremendously
successful program at Super-Kamiokande using a detector that is 20-50 times
larger. The potential of such a detector to continue the study of astrophysical
neutrinos is considered and contrasted with the program for cubic kilometer
neutrino observatories.Comment: 4 pages Submitted to the Proceedings of the 2004 Neutrino Oscillation
Workshop, Otranto Ital
nature of the superdeformed band of and the evolution of the molecular structure
The relation between the superdeformed band of and molecular bands is studied by the deformed-base
antisymmetrized molecular dynamics with the Gogny D1S force. It is found that
the obtained superdeformed band members of have considerable
amount of the component. Above the superdeformed
band, we have obtained two excited rotational bands which have more prominent
character of the molecular band. These three
rotational bands are regarded as a series of
molecular bands which were predicted by using the unique
- optical potentil. As the excitation energy and principal
quantum number of the relative motion increase, the cluster structure becomes more prominent but at the same time, the band
members are fragmented into several states
Conductance of Disordered Wires with Symplectic Symmetry: Comparison between Odd- and Even-Channel Cases
The conductance of disordered wires with symplectic symmetry is studied by
numerical simulations on the basis of a tight-binding model on a square lattice
consisting of M lattice sites in the transverse direction. If the potential
range of scatterers is much larger than the lattice constant, the number N of
conducting channels becomes odd (even) when M is odd (even). The average
dimensionless conductance g is calculated as a function of system length L. It
is shown that when N is odd, the conductance behaves as g --> 1 with increasing
L. This indicates the absence of Anderson localization. In the even-channel
case, the ordinary localization behavior arises and g decays exponentially with
increasing L. It is also shown that the decay of g is much faster in the
odd-channel case than in the even-channel case. These numerical results are in
qualitative agreement with existing analytic theories.Comment: 4 page
Zn-doping effect on the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals
We report the magnetotransport properties of
Bi_{2}Sr_{2-x}La_{x}Cu_{1-z}Zn_{z}O_{6+\delta} (Zn-doped BSLCO) single crystals
with z of up to 2.2%. Besides the typical Zn-doping effects on the in-plane
resistivity and the Hall angle, we demonstrate that the nature of the
low-temperature normal state in the Zn-doped samples is significantly altered
from that in the pristine samples under high magnetic fields. In particular, we
observe nearly-isotropic negative magnetoresistance as well as an increase in
the Hall coefficient at very low temperatures in non-superconducting Zn-doped
samples, which we propose to be caused by the Kondo scattering from the local
moments induced by Zn impurities.Comment: 4 pages, 4 figures, final version (one reference added), published in
Phys. Rev.
The Fractional Quantum Hall States of Dirac Electrons in Graphene
We have investigated the fractional quantum Hall states for the Dirac
electrons in a graphene layer in different Landau levels. The relativistic
nature of the energy dispersion relation of the electrons in the graphene
significantly modifies the inter-electron interactions. This results in a
specific dependence of the ground state energy and the energy gaps for
electrons on the Landau level index. For the valley-polarized states, i.e. at
\nu =1/m, m being an odd integer, the energy gaps have the largest values in
the n=1 Landau level. For the valley-unpolarized states, e.g., for the 2/3
state, the energy gaps are suppressed for the n=1 Landau level as compared to
the n=0 level. For both the n=1 and n=0 Landau levels the ground state of the
2/3 system is fully valley-unpolarized.Comment: accepted for publication in Phys. Rev. Let
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