Transport in Bilayer Graphene: Calculations within a self-consistent Born approximation

The transport properties of a bilayer graphene are studied theoretically within a self-consistent Born approximation. The electronic spectrum is composed of $k$-linear dispersion in the low-energy region and $k$-square dispersion as in an ordinary two-dimensional metal at high energy, leading to a crossover between different behaviors in the conductivity on changing the Fermi energy or disorder strengths. We find that the conductivity approaches $2e^2/\pi^2\hbar$ per spin in the strong-disorder regime, independently of the short- or long-range disorder.Comment: 8 pages, 5 figure

Systematic evolution of the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6} in a wide doping range

Recently we have succeeded in growing a series of high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6} crystals in a wide range of carrier concentrations. The data of \rho_{ab}(T) and R_H(T) of those crystals show behaviors that are considered to be "canonical" to the cuprates. The optimum zero-resistance T_c has been raised to as high as 38 K, which is almost equal to the optimum T_c of La_{2-x}Sr_{x}CuO_{4}.Comment: 2 pages, 2 figures, to be published in Physics C (Proceedings of the International Conference on Materials and Mechanisms of Superconductivity, High Temperature Superconductors VI (M2S-HTSC-VI), Houston, Feb 20-25, 2000

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

16O+16O^{16}{\rm O} + ^{16}{\rm O} nature of the superdeformed band of 32S^{32}{\rm S} and the evolution of the molecular structure

The relation between the superdeformed band of $^{32}{\rm S}$ and $^{16}{\rm O} + ^{16}{\rm O}$ 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 $^{32}{\rm S}$ have considerable amount of the $^{16}{\rm O} + ^{16}{\rm O}$ component. Above the superdeformed band, we have obtained two excited rotational bands which have more prominent character of the $^{16}{\rm O} + ^{16}{\rm O}$ molecular band. These three rotational bands are regarded as a series of $^{16}{\rm O} + ^{16}{\rm O}$ molecular bands which were predicted by using the unique $^{16}{\rm O}$ -$^{16}{\rm O}$ optical potentil. As the excitation energy and principal quantum number of the relative motion increase, the $^{16}{\rm O} + ^{16}{\rm O}$ cluster structure becomes more prominent but at the same time, the band members are fragmented into several states

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 $n e^2/h$ has $|n|$ separated bunches of extended levels, at least for an integer $n \leq 2$. 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

Unconventional conductance plateau transitions in quantum Hall wires with spatially correlated disorder

Quantum transport properties in quantum Hall wires in the presence of spatially correlated random potential are investigated numerically. It is found that the potential correlation reduces the localization length associated with the edge state, in contrast to the naive expectation that the potential correlation increases it. The effect appears as the sizable shift of quantized conductance plateaus in long wires, where the plateau transitions occur at energies much higher than the Landau band centers. The scale of the shift is of the order of the strength of the random potential and is insensitive to the strength of magnetic fields. Experimental implications are also discussed.Comment: 5 pages, 4 figure