1,082 research outputs found
Conduction States with Vanishing Dimerization in Pt Nanowires on Ge(001) Observed with Scanning Tunneling Microscopy
The low-energy electronic properties of one-dimensional nanowires formed by
Pt atoms on Ge(001) are studied with scanning tunneling microscopy down to the
millivolt-regime. The chain structure exhibits various dimerized elements at
high tunneling bias, indicative of a substrate bonding origin rather than a
charge density wave. Unexpectedly, this dimerization becomes vanishingly small
when imaging energy windows close to the Fermi level with adequately low
tunneling currents. Evenly spaced nanowire atoms emerge which are found to
represent conduction states. Implications for the metallicity of the chains are
discussed.Comment: 4 pages, 4 figure
Photoemission of a doped Mott insulator: spectral weight transfer and qualitative Mott-Hubbard description
The spectral weight evolution of the low-dimensional Mott insulator TiOCl
upon alkali-metal dosing has been studied by photoelectron spectroscopy. We
observe a spectral weight transfer between the lower Hubbard band and an
additional peak upon electron-doping, in line with quantitative expectations in
the atomic limit for changing the number of singly and doubly occupied sites.
This observation is an unconditional hallmark of correlated bands and has not
been reported before. In contrast, the absence of a metallic quasiparticle peak
can be traced back to a simple one-particle effect.Comment: 4 pages, 4 figures, related theoretical work can be found in
arXiv:0905.1276; shortene
Band Mapping in One-Step Photoemission Theory: Multi-Bloch-Wave Structure of Final States and Interference Effects
A novel Bloch-waves based one-step theory of photoemission is developed
within the augmented plane wave formalism. Implications of multi-Bloch-wave
structure of photoelectron final states for band mapping are established.
Interference between Bloch components of initial and final states leads to
prominent spectral features with characteristic frequency dispersion
experimentally observed in VSe_2 and TiTe_2. Interference effects together with
a non-free-electron nature of final states strongly limit the applicability of
the common direct transitions band mapping approach, making the tool of
one-step analysis indispensable.Comment: 4 jpg figure
Pressure dependence of the Verwey transition in magnetite: an infrared spectroscopic point of view
We investigated the electronic and vibrational properties of magnetite at
temperatures from 300 K down to 10 K and for pressures up to 10 GPa by
far-infrared reflectivity measurements. The Verwey transition is manifested by
a drastic decrease of the overall reflectance and the splitting of the phonon
modes as well as the activation of additional phonon modes. In the whole
studied pressure range the down-shift of the overall reflectance spectrum
saturates and the maximum number of phonon modes is reached at a critical
temperature, which sets a lower bound for the Verwey transition temperature
T. Based on these optical results a pressure-temperature phase
diagram for magnetite is proposed.Comment: 5 pages, 4 figures; accepted for publication in J. Appl. Phy
Heat capacity of the quantum magnet TiOCl
Measurements of the heat capacity C(T,H) of the one-dimensional quantum
magnet TiOCl are presented for temperatures 2K < T < 300K and magnetic fields
up to 5T. Distinct anomalies at 91K and 67K signal two subsequent phase
transitions. The lower of these transitions clearly is of first order and seems
to be related to the spin degrees of freedom. The transition at 92K probably
involves the lattice and/or orbital moments. A detailed analysis of the data
reveals that the entropy change through both transitions is surprisingly small
(~ 0.1R), pointing to the existence strong fluctuations well into the
non-ordered high-temperature phase. No significant magnetic field dependence
was detected.Comment: 4 pages, 2 figure
Structural Examination of Au/Ge(001) by Surface X-Ray Diffraction and Scanning Tunneling Microscopy
The one-dimensional reconstruction of Au/Ge(001) was investigated by means of
autocorrelation functions from surface x-ray diffraction (SXRD) and scanning
tunneling microscopy (STM). Interatomic distances found in the SXRD-Patterson
map are substantiated by results from STM. The Au coverage, recently determined
to be 3/4 of a monolayer of gold, together with SXRD leads to three
non-equivalent positions for Au within the c(8x2) unit cell. Combined with
structural information from STM topography and line profiling, two building
blocks are identified: Au-Ge hetero-dimers within the top wire architecture and
Au homo-dimers within the trenches. The incorporation of both components is
discussed using density functional theory and model based Patterson maps by
substituting Germanium atoms of the reconstructed Ge(001) surface.Comment: 5 pages, 3 figure
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