94 research outputs found
Electronic properties of metal induced gap states at insulator/metal interfaces -- dependence on the alkali halide and the possibility of excitonic mechanism of superconductivity
Motivated from the experimental observation of metal induced gap states
(MIGS) at insulator/metal interfaces by Kiguchi {\it et al.} [Phys. Rev. Lett.
{\bf 90}, 196803 (2003)], we have theoretically investigated the electronic
properties of MIGS at interfaces between various alkali halides and a metal
represented by a jellium with the first-principles density functional method.
We have found that, on top of the usual evanescent state, MIGS generally have a
long tail on halogen sites with a -like character, whose penetration depth
() is as large as half the lattice constant of bulk alkali halides.
This implies that , while little dependent on the carrier density in
the jellium, is dominated by the lattice constant (hence by energy gap) of the
alkali halide, where . We also propose a possibility of the MIGS working favorably for the
exciton-mediated superconductivity.Comment: 7 pages, 9 figure
THE TIGHT-BINDING APPROACH TO THE DIELECTRIC RESPONSE IN THE MULTIBAND SYSTEMS
Starting from the random phase approximation for the weakly coupled multiband
tightly-bounded electron systems, we calculate the dielectric matrix in terms
of intraband and interband transitions. The advantages of this representation
with respect to the usual plane-wave decomposition are pointed out. The
analysis becomes particularly transparent in the long wavelength limit, after
performing the multipole expansion of bare Coulomb matrix elements. For
illustration, the collective modes and the macroscopic dielectric function for
a general cubic lattice are derived. It is shown that the dielectric
instability in conducting narrow band systems proceeds by a common softening of
one transverse and one longitudinal mode. Furthermore, the self-polarization
corrections which appear in the macroscopic dielectric function for finite band
systems, are identified as a combined effect of intra-atomic exchange
interactions between electrons sitting in different orbitals and a finite
inter-atomic tunneling.Comment: 20 pages, LaTeX, no figure
Lattice dielectric response of CdCu{3}Ti{4}O{12} and of CaCu{3}Ti{4}O{12} from first principles
Structural, vibrational, and lattice dielectric properties of
CdCu{3}Ti{4}O{12} are studied using density-functional theory within the local
spin-density approximation, and the results are compared with those computed
previously for CaCu{3}Ti{4}O{12}. Replacing Ca with Cd is found to leave many
calculated quantities largely unaltered, although significant differences do
emerge in zone-center optical phonon frequencies and mode effective charges.
The computed phonon frequencies of CdCu{3}Ti{4}O{12} are found to be in
excellent agreement with experiment, and the computed lattice contribution to
the intrinsic static dielectric constant (~60) also agrees exceptionally well
with a recent optical absorption experiment. These results provide further
support for a picture in which the lattice dielectric response is essentially
conventional, suggesting an extrinsic origin for the anomalous low-frequency
dielectric response recently observed in both materials.Comment: 5 pages; uses REVTEX macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_cdct/index.htm
Theoretical Study of One-dimensional Chains of Metal Atoms in Nanotubes
Using first-principles total-energy pseudopotential calculations, we have
studied the properties of chains of potassium and aluminum in nanotubes. For BN
tubes, there is little interaction between the metal chains and the tubes, and
the conductivity of these tubes is through carriers located at the inner part
of the tube. In contrast, for small radius carbon nanotubes, there are two
types of interactions: charge-transfer (dominant for alkali atoms) leading to
strong ionic cohesion, and hybridization (for multivalent metal atoms)
resulting in a smaller cohesion. For Al-atomic chains in carbon tubes, we show
that both effects contribute. New electronic properties related to these
confined atomic chains of metal are analyzed.Comment: 12 pages + 3 figure
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