31 research outputs found
Induced Charge-Density Oscillations at Metal Surfaces
Induced charge-density (ICD) oscillations at the Cu(111) surface caused by an
external impurity are studied within linear response theory. The calculation
takes into account such properties of the Cu(111) surface electronic structure
as an energy gap for three-dimensional (3D) bulk electrons and a
surface state that forms two-dimensional (2D) electron system. It is
demonstrated that the coexistence of these 2D and 3D electron systems has
profound impact on the ICD in the surface region. In the case of a static
impurity the characteristic ICD oscillations with the decay as a
function of lateral distance, , are established in both electron systems.
For the impurity with a periodically time-varying potential, the novel dominant
ICD oscillations which fall off like are predicted.Comment: 11 pages, 5 figure
Surface and Image-Potential States on the MgB_2(0001) Surfaces
We present a self-consistent pseudopotential calculation of surface and
image-potential states on for both -terminated () and
-terminated () surfaces. We find a variety of very clear surface and
subsurface states as well as resonance image-potential states n=1,2 on both
surfaces. The surface layer DOS at is increased by 55% at and by
90% at the surface compared to DOS in the corresponding bulk layers.Comment: 3 pages, 6 figure
A first-principles study of MgB2 (0001) surfaces
We report self-consistent {\it ab initio} calculations of structural and
electronic properties for the B- and Mg-terminated MgB (0001) surfaces.
We employ ultra-soft pseudopotentials and plane wave basis sets within the
generalized gradient approximation. The surface relaxations are found to be
small for both B- and Mg-terminated surfaces. For the B-terminated surface,
both B and surface bands appear, while only one B
surface band exists near the Fermi level for the Mg-terminated surface. The
superconductivity of the MgB surfaces is discussed. The work function is
predicted to be 5.95 and 4.25 eV for the B- and Mg-terminated surfaces
respectively. The simulated scanning tunneling microscopy images of the
surfaces are not sensitive to the sign and value of the bias voltages, but
depend strongly on the tip-sample distance. An image reversal is predicted for
the Mg-terminated surface.Comment: 3 pages, 4 figures, Revte
Surface states and their possible role in the superconductivity of MgB2
We report layer-Korringa-Kohn-Rostocker calculations for bulk and surface
states as well as the corresponding angle resolved photoemission (ARPES)
intensities of MgB2. Our theoretical results reproduce very well the recent
ARPES data by Uchiyama et al., cond-mat/0111152. At least two surface states
are assigned. Consequences of SFS on the anisotropy of the upper critical
fields and other properties in the superconducting state of small grains in
micropowder samples are briefly discussed.Comment: 4pages, 6figures, corrected typos, references adde
Quasiparticle dynamics in ferromagnetic compounds of the Co-Fe and Ni-Fe systems
We report a theoretical study of the quasiparticle lifetime and the
quasiparticle mean free path caused by inelastic electron-electron scattering
in ferromagnetic compounds of the Co-Fe and Ni-Fe systems. The study is based
on spin-polarized calculations, which are performed within the
approximation for equiatomic and Co- and Ni-rich compounds, as well as for
their constituents. We mainly focus on the spin asymmetry of the quasiparticle
properties, which leads to the spin-filtering effect experimentally observed in
spin-dependent transport of hot electrons and holes in the systems under study.
By comparing with available experimental data on the attenuation length, we
estimate the contribution of the inelastic mean free path to the latter.Comment: 10 pages, 10 figure