131 research outputs found
Pulsed laser deposition of atomically flat La1-xSrxMnO3 thin films using a novel target geometry
A new ablation target geometry is presented that was used to produce thin films of La1-xSrxMnO3 grown heteroepitaxially on SrTiO3 by pulsed reactive crossed-beam laser ablation. The films were grown in order to perform angle-resolved photoelectron spectroscopy, which demands that the surface be atomically flat. In situ and ex situ analysis shows that this condition was met, even after depositing to a thickness of over 100n
The electronic structure of LaSrMnO thin films and its dependence as studied by angle-resolved photoemission
We present angle-resolved photoemission spectroscopy results for thin films
of the three-dimensional manganese perovskite LaSrMnO. We
show that the transition temperature () from the paramagnetic insulating
to ferromagnetic metallic state is closely related to details of the electronic
structure, particularly to the spectral weight at the -point, where
the sharpest step at the Fermi level was observed. We found that this -point is the same for all the samples, despite their different . The
change of is discussed in terms of kinetic energy optimization. Our ARPES
results suggest that the change of the electronic structure for the samples
having different transition temperatures is different from the rigid band
shift.Comment: Accepted by Journal of Physics: Condensed Matte
Giant Spin-splitting in the Bi/Ag(111) Surface Alloy
Surface alloying is shown to produce electronic states with a very large
spin-splitting. We discuss the long range ordered bismuth/silver(111) surface
alloy where an energy bands separation of up to one eV is achieved. Such strong
spin-splitting enables angular resolved photoemission spectroscopy to directly
observe the region close to the band edge, where the density of states shows
quasi-one dimensional behavior. The associated singularity in the local density
of states has been measured by low temperature scanning tunneling spectroscopy.
The implications of this new class of materials for potential spintronics
applications as well as fundamental issues are discussed.Comment: 4 pages, 4 figure
Fermi Surface and Quasiparticle Excitations of overdoped Tl2Ba2CuO6+d by ARPES
The electronic structure of the high-T_c superconductor Tl2Ba2CuO6+d is
studied by ARPES. For a very overdoped Tc=30K sample, the Fermi surface
consists of a single large hole pocket centered at (pi,pi) and is approaching a
topological transition. Although a superconducting gap with d_x^2-y^2 symmetry
is tentatively identified, the quasiparticle evolution with momentum and
binding energy exhibits a marked departure from the behavior observed in under
and optimally doped cuprates. The relevance of these findings to scattering,
many-body, and quantum-critical phenomena is discussed.Comment: Revised manuscript, in press on PRL. A high-resolution version can be
found at
http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/Tl2201_LE.pdf
and related material at
http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/articles.htm
Parity of the Pairing Bosons in a High-Temperature Superconductor
We report the observation of a novel effect in the bilayer Pb-Bi2212 high-TC
superconductor by means of angle-resolved photoemission with circularly
polarized excitation. Different scattering rates, determined as a function of
energy separately for the bonding and antibonding copper-oxygen bands, strongly
imply that the dominating scattering channel is odd with respect to layer
exchange within a bilayer. This is inconsistent with a phonon-mediated
scattering and favours the participation of the odd collective spin excitations
in the scattering mechanism in near-nodal regions of the k-space, suggesting a
magnetic nature of the pairing mediator.Comment: 5 RevTex pages, 4 eps figure
Total Angular Momentum Conservation During Tunnelling through Semiconductor Barriers
We have investigated the electrical transport through strained
p-Si/Si_{1-x}Ge_x double-barrier resonant tunnelling diodes. The confinement
shift for diodes with different well width, the shift due to a central
potential spike in a well, and magnetotunnelling spectroscopy demonstrate that
the first two resonances are due to tunnelling through heavy hole levels,
whereas there is no sign of tunnelling through the first light hole state. This
demonstrates for the first time the conservation of the total angular momentum
in valence band resonant tunnelling. It is also shown that conduction through
light hole states is possible in many structures due to tunnelling of carriers
from bulk emitter states.Comment: 4 pages, 4 figure
X-Ray Nano-Diffraction on Epitaxial Crystals
The concept of growing epitaxial Ge and SiGe crystals onto tall Si pillars may provide a means for solving the problems associated with lattice parameter and thermal expansion coefficient mismatch, i.e., dislocations, wafer bowing and cracks. For carefully tuned epitaxial growth conditions the lateral expansion of crystals stops once nearest neighbors get sufficiently close. We have carried out scanning nano-diffraction experiments at the ID01 beam-line of the European Synchrotron Radiation Facility (ESRF) in Grenoble on the resulting space-filling arrays of micron-sized crystals to assess their structural properties and crystal quality. Elastic relaxation of the thermal strain causes lattice bending close to the Si interface, while the dislocation network is responsible for minute tilts of the crystals as a whole. To exclude any interference from nearest neighbors, individual Ge crystals were isolated first by chemical etching followed by micro-manipulation inside a scanning electron microscope. This permitted us to scan an X-ray beam, focused to a spot a few hundreds of nm in size, along the height of a single crystal and to record three-dimensional reciprocal space maps at chosen heights. The resolution limited width of the scattered X-ray beams reveals that the epitaxial structures evolve into perfect single crystals sufficiently far away from the heavily dislocated interface
Scaling hetero-epitaxy from layers to three-dimensional crystals
Laying It on Thick
The growth of one layered material onto a second lies at the heart of many electronic devices. However, if there is a lattice mismatch between the two materials, strains develop in the overgrowth material leading to bowing and cracking.
Falub
et al.
(p.
1330
; see the cover) patterned Si substrates into a series of pillars onto which they grew a germanium layer. The germanium initially coated the top of each silicon pillar but then widened as the layer thickened, leading to thick, crack-free germanium films.
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