7,805 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
Quantum oscillations in a topological insulator Bi_{1-x}Sb_{x}
We have studied transport and magnetic properties of Bi_{1-x}Sb_x, which is
believed to be a topological insulator - a new state of matter where an
insulating bulk supports an intrinsically metallic surface. In nominally
insulating Bi_{0.91}Sb_{0.09} crystals, we observed strong quantum oscillations
of the magnetization and the resistivity originating from a Fermi surface which
has a clear two-dimensional character. In addition, a three-dimensional Fermi
surface is found to coexist, which is possibly due to an unusual coupling of
the bulk to the surface. This finding demonstrates that quantum oscillations
can be a powerful tool to directly probe the novel electronic states in
topological insulators.Comment: 4 pages, 4 figure
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
Coherence and superconductivity in coupled one-dimensional chains: a case study of YBaCuO
We report the infrared (IR) response of Cu-O chains in the high-
superconductor YBaCuO over the doping range spanning . We find evidence for a power law scaling at mid-IR frequencies
consistent with predictions for Tomonaga-Luttinger liquid, thus supporting the
notion of one-dimensional transport in the chains. We analyze the role of
coupling to the CuO planes in establishing metallicity and
superconductivity in disordered chain fragments.Comment: 4 pages, 3 figure
Contact resistance and shot noise in graphene transistors
Potential steps naturally develop in graphene near metallic contacts. We
investigate the influence of these steps on the transport in graphene Field
Effect Transistors. We give simple expressions to estimate the
voltage-dependent contribution of the contacts to the total resistance and
noise in the diffusive and ballistic regimes.Comment: 6 pages, 4 figures; Figs 3 and 4 completed and appendix adde
- …