488 research outputs found
Evidence for phase formation in potassium intercalated 1,2;8,9-dibenzopentacene
We have prepared potassium intercalated 1,2;8,9-dibenzopentacene films under
vacuum conditions. The evolution of the electronic excitation spectra upon
potassium addition as measured using electron energy-loss spectroscopy clearly
indicate the formation of particular doped phases with compositions
Kdibenzopentacene ( = 1,2,3). Moreover, the stability of these phases as
a function of temperature has been explored. Finally, the electronic excitation
spectra also give insight into the electronic ground state of the potassium
doped 1,2;8,9-dibenzopentacene films.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1201.200
Transition from a Tomonaga-Luttinger liquid to a Fermi liquid in potassium intercalated bundles of single wall carbon nanotubes
We report on the first direct observation of a transition from a
Tomonaga-Luttinger liquid to a Fermi liquid behavior in potassium intercalated
mats of single wall carbon nanotubes (SWCNT). Using high resolution
photoemission spectroscopy an analysis of the spectral shape near the Fermi
level reveals a Tomonaga-Luttinger liquid power law scaling in the density of
states for the pristine sample and for low dopant concentration. As soon as the
doping is high enough to fill bands of the semiconducting tubes a distinct
transition to a bundle of only metallic SWCNT with a scaling behavior of a
normal Fermi liquid occurs. This can be explained by a strong screening of the
Coulomb interaction between charge carriers and/or an increased hopping matrix
element between the tubes.Comment: 5 pages, 4 figure
Manifestation of spin-charge separation in the dynamic dielectric response of one--dimensional Sr2CuO3
We have determined the dynamical dielectric response of a one-dimensional,
correlated insulator by carrying out electron energy-loss spectroscopy on
Sr2CuO3 single crystals. The observed momentum and energy dependence of the
low-energy features, which correspond to collective transitions across the gap,
are well described by an extended one-band Hubbard model with moderate nearest
neighbor Coulomb interaction strength. An exciton-like peak appears with
increasing momentum transfer. These observations provide experimental evidence
for spin-charge separation in the relevant excitations of this compound, as
theoretically expected for the one-dimensional Hubbard model.Comment: RevTex, 4 pages+2 figures, to appear in PRL (July 13
Fine-tuning the functional properties of carbon nanotubes via the interconversion of encapsulated molecules
Tweaking the properties of carbon nanotubes is a prerequisite for their
practical applications. Here we demonstrate fine-tuning the electronic
properties of single-wall carbon nanotubes via filling with ferrocene
molecules. The evolution of the bonding and charge transfer within the tube is
demonstrated via chemical reaction of the ferrocene filler ending up as
secondary inner tube. The charge transfer nature is interpreted well within
density functional theory. This work gives the first direct observation of a
fine-tuned continuous amphoteric doping of single-wall carbon nanotubes
The electronic structure of the organic semiconductor copper phthalocyanine (CuPc) and K-CuPc studied using photoemission spectroscopy
X-ray absorption spectroscopy on layered cobaltates Na_xCoO_2
Measurements of polarization and temperature dependent soft x-ray absorption
have been performed on Na_xCoO_2 single crystals with x=0.4 and x=0.6. They
show a deviation of the local trigonal symmetry of the CoO_6 octahedra, which
is temperature independent in a temperature range between 25 K and 372 K. This
deviation was found to be different for Co^{3+} and Co^{4+} sites. With the
help of a cluster calculation we are able to interpret the Co L_{23}-edge
absorption spectrum and find a doping dependent energy splitting between the
t_{2g} and the e_g levels (10Dq) in Na_xCoO_2.Comment: 7 pages, 8 figure
Plasmon Evolution and Charge-Density Wave Suppression in Potassium Intercalated Tantalum Diselenide
We have investigated the influence of potassium intercalation on the
formation of the charge-density wave (CDW) instability in 2H-tantalum
diselenide by means of Electron Energy-Loss Spectroscopy and density functional
theory. Our observations are consistent with a filling of the conduction band
as indicated by a substantial decrease of the plasma frequency in experiment
and theory. In addition, elastic scattering clearly points to a destruction of
the CDW upon intercalation as can be seen by a vanishing of the corresponding
superstructures. This is accompanied by a new superstructure, which can be
attributed to the intercalated potassium. Based on the behavior of the c-axis
upon intercalation we argue in favor of interlayer-sites for the alkali-metal
and that the lattice remains in the 2H-modification
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