975 research outputs found
Non-Commutative Tools for Topological Insulators
This paper reviews several analytic tools for the field of topological
insulators, developed with the aid of non-commutative calculus and geometry.
The set of tools includes bulk topological invariants defined directly in the
thermodynamic limit and in the presence of disorder, whose robustness is shown
to have non-trivial physical consequences for the bulk states. The set of tools
also includes a general relation between the current of an observable and its
edge index, relation that can be used to investigate the robustness of the edge
states against disorder. The paper focuses on the motivations behind creating
such tools and on how to use them.Comment: Final version (some arguments were corrected
Electronic structure and optical properties of metallic nanoshells
The electronic structure and optical properties of metallic nanoshells are
investigated using a jellium model and the Time Dependent Local Density
Approximation (TDLDA). An efficient numerical implementation enables
applications to nanoshells of realistic size with up to a million electrons. We
demonstrate how a frequency dependent background polarizability of the jellium
shell can be included in the TDLDA formalism. The energies of the plasmon
resonances are calculated for nanoshells of different sizes and with different
dielectric cores, dielectric embedding media, and dielectric shell backgrounds.
The plasmon energies are found to be in good agreement with the results from
classical Mie scattering theory using a Drude dielectric function. A comparison
with experimental data shows excellent agreement between theory and the
measured frequency dependent absorption spectra
Band Alignment in Molecular Devices: Influence of Anchoring Group and Metal Work Function
We present periodic Density Functional Theory calculations of the electronic
properties of molecular junctions formed by amine-, and thiol-terminated alkane
chains attached to two metal (Au, Ag) electrodes. Based on extensive analysis
that includes molecular monolayers of varying densities, we establish a
relationship between the alignment of the molecular energy levels and the
interface dipoles, which shows that the band alignment (BA) in the limit of
long, isolated chains is independent of the link group and can be computed from
a reference system of non interacting molecule + metal electrodes. The main
difference between the amine and thiol linkers is the effective dipole moment
at the contact. This is very large, about 4.5 D, for amine linkers, leading to
a strong dependence of the BA on the monolayer density and a slow convergence
to the isolated molecule limit. Instead, this convergence is fast for S anchors
due to the very small, ~ 0.2 D, effective dipoles at the contacts
Transfer matrices for scalar fields on curved spaces
We apply Nelson's technique of constructing Euclidean fields to the case of
classical scalar fields on curved spaces. It is shown how to construct a
transfer matrix and, for a class of metrics, the basic spectral properties of
its generator are investigated. An application concerning decoupling of
non-convex disjoint region is given.Comment: 11 pages, no figur
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