Edge States and Quantum Hall Effect in Graphene under a Modulated Magnetic Field

Graphene properties can be manipulated by a periodic potential. Based on the tight-binding model, we study graphene under a one-dimensional (1D) modulated magnetic field which contains both a uniform and a staggered component. New chiral current-carrying edge states are generated at the interfaces where the staggered component changes direction. These edge states lead to an unusual integer quantum Hall effect (QHE) in graphene, which can be observed experimentally by a standard four-terminal Hall measurement. When Zeeman spin splitting is considered, a novel state is predicted where the electron edge currents with opposite polarization propagate in the opposite directions at one sample boundary, whereas propagate in the same directions at the other sample boundary.Comment: 5 pages, 4 figure

Common Stochastic Trends, Common Cycles, and Asymmetry in Economic Fluctuations

We investigate the nature of asymmetries in U.S. business cycle dynamics using a dynamic two-factor model of output, investment, and consumption that incorporates both the common stochastic trend implied by neoclassical growth theory and a common transitory component. This framework allows for identification of both types of asymmetry commonly identified in the literature: 1. Shifts in the growth rate of the trend component and 2. Transitory deviations below trend, or "plucking". The model also lends itself easily to tests of the marginal significance of each type of asymmetry when the other is allowed to be present. Such tests suggest that both types of asymmetries have played a significant role in post-war recessions, although the nature of shifts in the growth rate of trend is different than the received literature suggests. We also allow for a one-time structural break in the long run growth rate of the common stochastic trend (a productivity slowdown) and in the magnitude of the asymmetry parameters. We find evidence of a productivity slowdown and an increase in the relative importance of shifts in the common stochastic trend vs. the "plucking" type of asymmetry. The evidence suggests a gradual structural break which begins in the mid 1960's and is complete by the end of 1973.