188 research outputs found
Topological States on the Gold Surface
Gold surfaces host special electronic states that have been understood as a
prototype of Shockley surface states (SSs). These SSs are commonly employed to
benchmark the capability of angle-resolved photoemission spectroscopy (ARPES)
and scanning tunneling spectroscopy. We find that these Shockley SSs can be
reinterpreted as topologically derived surface states (TDSSs) of a topological
insulator (TI), a recently discovered quantum state. Based on band structure
calculations, the Z2 topological invariant can be well defined to characterize
the nontrivial features of gold that we detect by ARPES. The same TDSSs are
also recognized on surfaces of other well-known noble metals (e.g., silver,
copper, platinum, and palladium). Besides providing a new understanding of
noble metal SSs, finding topological states on late transition metals provokes
interesting questions on the role of topological effects in surface-related
processes, such as adsorption and catalysis.Comment: 21 pages, 3 figure
Light-induced magnetization reversal of high-anisotropy TbCo alloy films
Magnetization reversal using circularly polarized light provides a new way to
control magnetization without any external magnetic field and has the potential
to revolutionize magnetic data storage. However, in order to reach ultra-high
density data storage, high anisotropy media providing thermal stability are
needed. Here, we evidence all-optical magnetization switching for different
TbxCo1-x ferrimagnetic alloy composition and demonstrate all-optical switching
for films with anisotropy fields reaching 6 T corresponding to anisotropy
constants of 3x106 ergs/cm3. Optical magnetization switching is observed only
for alloys which compensation temperature can be reached through sample
heating
Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films
We have studied the possibly half metallic Co2FeSi full Heusler alloy by
means of spin- and time-resolved photoemission spectroscopy. For excitation,
the second and fourth harmonic of femtosecond Ti:sapphire lasers were used,
with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the
dependence of the measured surface spin polarization on the particular
photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon
photoemission (2PPE). The observed differences in the spin polarization can be
explained by a spin-dependent lifetime effect occurring in the 2-photon
absorption process. The difference in escape depth of the two methods in this
context suggests that the observed reduction of spin polarization (compared to
the bulk) cannot be attributed just to the outermost surface layer but takes
place at least 4-6 nm away from the surface.Comment: 7 pages, 3 figures; submitted to Journal of Magnetism and Magnetic
Material
Electronic and magnetic properties of the interface between metal-quinoline molecules and cobalt
Photoemission Electron Microscopy as a tool for the investigation of optical near fields
Photoemission electron microscopy was used to image the electrons
photoemitted from specially tailored Ag nanoparticles deposited on a Si
substrate (with its native oxide SiO). Photoemission was induced by
illumination with a Hg UV-lamp (photon energy cutoff eV,
wavelength nm) and with a Ti:Sapphire femtosecond laser
( eV, nm, pulse width below 200 fs),
respectively. While homogeneous photoelectron emission from the metal is
observed upon illumination at energies above the silver plasmon frequency, at
lower photon energies the emission is localized at tips of the structure. This
is interpreted as a signature of the local electrical field therefore providing
a tool to map the optical near field with the resolution of emission electron
microscopy.Comment: 10 pages, 4 figures; submitted to Physical Review Letter
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