7 research outputs found
STM Study on Two-Dimensional Electronic System Localized on Surfaces(STM-local states)
There are some surface electronic states which can be regarded as two dimensional electronic system. Their properties have been studied using novel techniques of scanning tunneling microscopy (STM). Two examples of such surfaces; Si(111)7x7 structure and Au(111), are presented. It was found that behavior of electrons in such states are strongly affected by chemical (adsorbates) and morphological (steps or islands) properties of the surfaces
Visualizing Orbital Content of Electronic Bands in Anisotropic 2D Semiconducting ReSe2
Many properties of layered materials change as they are thinned from their
bulk forms down to single layers, with examples including indirect-to-direct
band gap transition in 2H semiconducting transition metal dichalcogenides as
well as thickness-dependent changes in the valence band structure in
post-transition metal monochalcogenides and black phosphorus. Here, we use
angle-resolved photoemission spectroscopy to study the electronic band
structure of monolayer ReSe, a semiconductor with a distorted 1T
structure and in-plane anisotropy. By changing the polarization of incoming
photons, we demonstrate that for ReSe, in contrast to the 2H materials,
the out-of-plane transition metal and chalcogen orbitals do
not contribute significantly to the top of the valence band which explains the
reported weak changes in the electronic structure of this compound as a
function of layer number. We estimate a band gap of 1.7 eV in pristine
ReSe using scanning tunneling spectroscopy and explore the implications
on the gap following surface-doping with potassium. A lower bound of 1.4 eV is
estimated for the gap in the fully doped case, suggesting that doping-dependent
many-body effects significantly affect the electronic properties of ReSe.
Our results, supported by density functional theory calculations, provide
insight into the mechanisms behind polarization-dependent optical properties of
rhenium dichalcogenides and highlight their place amongst two-dimensional
crystals.Comment: 37 pages (including Supporting Information), 7 figures in the main
tex
Why is the bandwidth of sodium observed to be narrower in photoemission experiments?
The experimentally predicted narrowing in the bandwidth of sodium is
interpreted in terms of the non-local self-energy effect on quasi-particle
energies of the electron liquid. The calculated self-energy correction is a
monotonically increasing function of the wavenumber variable. The usual
analysis of photo-emission experiments assumes the final state energies on the
nearly-free-electron-like model and hence it incorrectly ascribes the non-local
self-energy correction to the final state energies to the occupied state
energies, thus leading to a seeming narrowing in the bandwidth.Comment: 9 page