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

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

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

Metal-to-Insulator Crossover in the Low-Temperature Normal State of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta}

We measure the normal-state in-plane resistivity of La-doped Bi-2201 single crystals at low temperatures by suppressing superconductivity with 60-T pulsed magnetic fields. With decreasing hole doping, we observe a crossover from a metallic to insulating behavior in the low-temperature normal state. This crossover is estimated to occur near 1/8 doping, well inside the underdoped regime, and not at optimum doping as reported for other cuprates. The insulating regime is marked by a logarithmic temperature dependence of the resistivity over two decades of temperature, suggesting that a peculiar charge localization is common to the cuprates.Comment: 4 pages, 5 figures, accepted for publication in PR

Fees in an Imperfect World: An Application to Motor Vehicle Emissions

This paper compares an emissions fee on measured vehicle emissions rates to a mandatory regulation that requires all vehicles to maintain emissions below a minimum standard. We model the motorist’s decision under the fee policy and simulate the fee and regulatory policies using data from an emissions inspection program that includes test and repair information for more than 50,000 vehicles. Under ideal conditions with perfect information and no subsidies, the fee on emissions rates performs substantially better than the regulatory policy. When more realistic modeling of available information and market conditions are included, there is little difference in the cost and effectiveness of the fee and regulatory programs. In particular, we find that the ability of the polluter to assess the emissions and cost outcomes of is critical importance for the performance of the fee policy.pollution fees, emissions control, vehicle pollution, inspection and maintenance

Coherence and superconductivity in coupled one-dimensional chains: a case study of YBa2_{2}Cu3_{3}Oy_{y}

We report the infrared (IR) response of Cu-O chains in the high-$T_{c}$ superconductor YBa$_{2}$Cu$_{3}$O$_{y}$ over the doping range spanning $y=6.28-6.75$. 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$_{2}$ planes in establishing metallicity and superconductivity in disordered chain fragments.Comment: 4 pages, 3 figure

Oscillatory angular dependence of the magnetoresistance in a topological insulator Bi_{1-x}Sb_{x}

The angular-dependent magnetoresistance and the Shubnikov-de Haas oscillations are studied in a topological insulator Bi_{0.91}Sb_{0.09}, where the two-dimensional (2D) surface states coexist with a three-dimensional (3D) bulk Fermi surface (FS). Two distinct types of oscillatory phenomena are discovered in the angular-dependence: The one observed at lower fields is shown to originate from the surface state, which resides on the (2\bar{1}\bar{1}) plane, giving a new way to distinguish the 2D surface state from the 3D FS. The other one, which becomes prominent at higher fields, probably comes from the (111) plane and is obviously of unknown origin, pointing to new physics in transport properties of topological insulators.Comment: 4 pages, 5 figures, revised version with improved data and analysi

Self-Consistent Electron Subbands of Gaas/Algaas Heterostructure in Magnetic Fields Parallel to the Interface

The effect of strong magnetic fields parallel to GaAs/AlGaAs interface on the subband structure of a 2D electron layer is ivestigated theoretically. The system with two levels occupied in zero magnetic field is considered and the magnetic field induced depletion of the second subband is studied. The confining potential and the electron dispersion relations are calculated self-consistently, the electron- electron interaction is taken into account in the Hartree approximation.Comment: written in LaTeX, 8 pages, 4 figs. available on request from [email protected]