538 research outputs found
Zero modes, energy gap, and edge states of anisotropic honeycomb lattice in a magnetic field
We present systematic study of zero modes and gaps by introducing effects of
anisotropy of hopping integrals for a tight-binding model on the honeycomb
lattice in a magnetic field. The condition for the existence of zero modes is
analytically derived. From the condition, it is found that a tiny anisotropy
for graphene is sufficient to open a gap around zero energy in a magnetic
field. This gap behaves as a non-perturbative and exponential form as a
function of the magnetic field. The non-analytic behavior with respect to the
magnetic field can be understood as tunneling effects between energy levels
around two Dirac zero modes appearing in the honeycomb lattice, and an explicit
form of the gap around zero energy is obtained by the WKB method near the
merging point of these Dirac zero modes. Effects of the anisotropy for the
honeycomb lattices with boundaries are also studied. The condition for the
existence of zero energy edge states in a magnetic field is analytically
derived. On the basis of the condition, it is recognized that anisotropy of the
hopping integrals induces abrupt changes of the number of zero energy edge
states, which depend on the shapes of the edges sensitively.Comment: 36 pages, 20 figures; added discussion on experiments in Sec.VI,
cited Refs.[35]-[40], and reworded Sec.IV
Self-sustained annihilation of magnetic islands in helical plasmas
The evolution of the magnetic island which is induced by the resonant deformation by external currents in helical systems (such as the large helical device (LHD) [A. Iiyoshi, Phys. Plasmas 2, 2349 (1995)]) is analyzed. The defect of the bootstrap current, caused by the magnetic island, has a parity which reduces the size of the magnetic island, if the bootstrap current enhances the vacuum rotational transform. The width of magnetic island can be suppressed to the level of ion banana width if the pressure gradient exceeds a threshold value. This island annihilation is self-sustained. That is, the annihilation continues, for fixed beta value, until the external drive for island generation exceeds a threshold. The effects of the reversal of the direction of the bootstrap current and of the sign of radial electric field are also investigated. The possibility of the neoclassical tearing mode in the LHD-like plasma is discussed
Transition Probability to Turbulent Transport Regime
Transition phenomena between thermal noise state and turbulent state observed
in a submarginal turbulent plasma are analyzed with statistical theory.
Time-development of turbulent fluctuation is obtained by numerical simulations
of Langevin equation which contains hysteresis characteristics. Transition
rates between two states are analyzed. Transition from turbulent state to
thermal noise state occurs in entire region between subcritical bifurcation
point and linear stability boundary.Comment: 9 pages, 6 figures, to be published in Plasma Phys. Control. Fusio
Selective formation of turbulent structures in magnetized cylindrical plasmas
The mechanism of nonlinear structural formation has been studied with a three-field reduced fluid model, which is extended to describe the resistive drift wave turbulence in magnetized cylindrical plasmas. In this model, ion-neutral collisions strongly stabilize the resistive drift wave, and the formed structure depends on the collision frequency. If the collision frequency is small, modulational coupling of unstable modes generates a zonal flow. On the other hand, if the collision frequency is large, a streamer, which is a localized vortex in the azimuthal direction, is formed. The structure is generated by nonlinear wave coupling and is sustained for a much longer duration than the drift wave oscillation period. This is a minimal model for analyzing the turbulent structural formation mechanism by mode coupling in cylindrical plasmas, and the competitive nature of structural formation is revealed. These turbulent structures affect particle transport
Non-Abelian Topological Order in S-Wave Superfluids of Ultracold Fermionic Atoms
We show that in s-wave superfluids of cold fermionic atoms with
laser-field-generated effective spin-orbit interactions, a topological phase
with gapless edge states and Majorana fermion quasiparticles obeying the
non-Abelian statistics is realized in the case with a large Zeeman magnetic
field. Our scenario provides a promising approach for quantum computation
manipulating non-Abelian anyons via an s-wave Feshbach resonance.Comment: 5 pages, 2 figures. Some minor improvements were mad
Nodal Structure of Superconductors with Time-Reversal Invariance and Z2 Topological Number
A topological argument is presented for nodal structures of superconducting
states with time-reversal invariance. A generic Hamiltonian which describes a
quasiparticle in superconducting states with time-reversal invariance is
derived, and it is shown that only line nodes are topologically stable in
single-band descriptions of superconductivity. Using the time-reversal
symmetry, we introduce a real structure and define topological numbers of line
nodes. Stability of line nodes is ensured by conservation of the topological
numbers. Line nodes in high-Tc materials, the polar state in p-wave paring and
mixed singlet-triplet superconducting states are examined in detail.Comment: 11 pages, 8 figure
Local Variations in Lunar Regolith Thickness: Testing a New Model of Regolith Formation near the Apollo 15 Site
No abstract availabl
Heisenberg realization for U_q(sln) on the flag manifold
We give the Heisenberg realization for the quantum algebra , which
is written by the -difference operator on the flag manifold. We construct it
from the action of on the -symmetric algebra by the
Borel-Weil like approach. Our realization is applicable to the construction of
the free field realization for the [AOS].Comment: 10 pages, YITP/K-1016, plain TEX (some mistakes corrected and a
reference added
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