83 research outputs found
Effect of Subband Landau Level Coupling to the Linearly Dispersing Collective Mode in a Quantum Hall Ferromagnet
In a recent experiment (Phys. Rev. Lett. {\bf 87}, 036903 (2001)), Spielman
et al observed a linearly dispersing collective mode in quantum Hall
ferromagnet. While it qualitatively agrees with the Goldstone mode dispersion
at small wave vector, the experimental mode velocity is slower than that
calculated by previous theories by a factor about 0.55. A better agreement with
the experimental data may possibly be achieved by taking the subband Landau
level coupling into account due to the finiteness of the layer thickness. A
novel coupling of quantum fluctuation to the tunneling is briefly discussed.Comment: 4 pages; published versio
Global phase diagram of bilayer quantum Hall ferromagnets
We present a microscopic study of the interlayer spacing d versus in-plane
magnetic field phase diagram for bilayer quantum Hall (QH)
pseudo-ferromagnets. In addition to the interlayer charge balanced commensurate
and incommensurate states analyzed previously, we address the corresponding
interlayer charge unbalanced "canted" QH states. We predict a large anomaly in
the bilayer capacitance at the canting transition and the formation of dipole
stripe domains with periods exceeding 1 micron in the canted state.Comment: 4 RevTeX pgs, 2 eps figures, submitted to PR
Fractionalization patterns in strongly correlated electron systems: Spin-charge separation and beyond
We discuss possible patterns of electron fractionalization in strongly
interacting electron systems. A popular possibility is one in which the charge
of the electron has been liberated from its Fermi statistics. Such a
fractionalized phase contains in it the seed of superconductivity. Another
possibility occurs when the spin of the electron, rather than its charge, is
liberated from its Fermi statistics. Such a phase contains in it the seed of
magnetism, rather than superconductivity. We consider models in which both of
these phases occur and study possible phase transitions between them. We
describe other fractionalized phases, distinct from these, in which fractions
of the electron themselves fractionalize, and discuss the topological
characterization of such phases. These ideas are illustrated with specific
models of p-wave superconductors, Kondo lattices, and coexistence between
d-wave superconductivity and antiferromagnetism.Comment: 28 pages, 11 fig
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
Scratch damage in ceramics: Role of microstructure
Scratch tests were conducted using a standard pyramid indenter against alpha-SiAlON ceramics with different microstructures: (i) fine equiaxed grains and (ii) large elongated grains. The formation and propagation of cracks were investigated via focused ion-beam milling, with an emphasis on the effect of microstructure on material removal. The fine equiaxed microstructure exhibited high resistance to material removal at low loads, because of its high hardness and homogeneous structure. As the load increased, radial and lateral cracks developed, resulting in large-scale chipping. In contrast, the large elongated microstructure showed a propensity to form micro-cracks and microabrasion, which is characteristic of partial grain removal, at low loads. With increasing loads, however, the large elongated grains suppressed the propagation of radial and lateral cracks, and, consequently, no large-scale chipping occurred. Implications for material design in abrasive-wear conditions have been discussed
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