1,459 research outputs found
Quantum Size Effect in Conductivity of Multilayer Metal Films
Conductivity of quantized multilayer metal films is analyzed with an emphasis
on scattering by rough interlayer interfaces. Three different types of quantum
size effect (QSE) in conductivity are predicted. Two of these QSE are similar
to those in films with scattering by rough walls. The third type of QSE is
unique and is observed only for certain positions of the interface. The
corresponding peaks in conductivity are very narrow and high with a finite
cutoff which is due only to some other scattering mechanism or the smearing of
the interface. There are two classes of these geometric resonances. Some of the
resonance positions of the interface are universal and do not depend on the
strength of the interface potential while the others are sensitive to this
potential. This geometric QSE gradually disappears with an increase in the
width of the interlayer potential barrier.Comment: 12 pages, 10 figures, RevTeX4, to be published in Phys. Rev B (April
2003
On the uniqueness of higher-spin symmetries in AdS and CFT
We study the uniqueness of higher-spin algebras which are at the core of
higher-spin theories in AdS and of CFTs with exact higher-spin symmetry, i.e.
conserved tensors of rank greater than two. The Jacobi identity for the gauge
algebra is the simplest consistency test that appears at the quartic order for
a gauge theory. Similarly, the algebra of charges in a CFT must also obey the
Jacobi identity. These algebras are essentially the same. Solving the Jacobi
identity under some simplifying assumptions spelled out, we obtain that the
Eastwood-Vasiliev algebra is the unique solution for d=4 and d>6. In 5d there
is a one-parameter family of algebras that was known before. In particular, we
show that the introduction of a single higher-spin gauge field/current
automatically requires the infinite tower of higher-spin gauge fields/currents.
The result implies that from all the admissible non-Abelian cubic vertices in
AdS(d), that have been recently classified for totally symmetric higher-spin
gauge fields, only one vertex can pass the Jacobi consistency test. This cubic
vertex is associated with a gauge deformation that is the germ of the
Eastwood-Vasiliev's higher-spin algebra.Comment: 37 pages; refs added, proof of uniquiness was improve
Non-abelian cubic vertices for higher-spin fields in AdS(d)
We use the Fradkin-Vasiliev procedure to construct the full set of non-abelian cubic vertices for totally symmetric higher spin gauge fields in anti-de Sitter space. The number of such vertices is given by a certain tensor-product multiplicity. We discuss the one-to-one relation between our result and the list of non-abelian gauge deformations in flat space obtained elsewhere via the cohomological approach. We comment about the uniqueness of Vasiliev's simplest higher-spin algebra in relation with the (non)associativity properties of the gauge algebras that we classified. The gravitational interactions for (partially)-massless (mixed)-symmetry fields are also discussed. We also argue that those mixed-symmetry and/or partially-massless fields that are described by one-form connections within the frame-like approach can have nonabelian interactions among themselves and again the number of nonabelian vertices should be given by tensor product multiplicities
Self-organized pore formation and open-loop-control in semiconductor etching
Electrochemical etching of semiconductors, apart from many technical
applications, provides an interesting experimental setup for self-organized
structure formation capable e.g. of regular, diameter-modulated, and branching
pores. The underlying dynamical processes governing current transfer and
structure formation are described by the Current-Burst-Model: all dissolution
processes are assumed to occur inhomogeneously in time and space as a Current
Burst (CB); the properties and interactions between CB's are described by a
number of material- and chemistry- dependent ingredients, like passivation and
aging of surfaces in different crystallographic orientations, giving a
qualitative understanding of resulting pore morphologies. These morphologies
cannot be influenced only by the current, by chemical, material and other
etching conditions, but also by an open-loop control, triggering the time scale
given by the oxide dissolution time. With this method, under conditions where
only branching pores occur, the additional signal hinders side pore formation
resulting in regular pores with modulated diameter
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