286 research outputs found
The band structure and Fermi surface of LaSrMnO thin films studied by in-situ angle-resolved photoemission spectroscopy
We have performed an in situ angle-resolved photoemission spectroscopy
(ARPES) on single-crystal surfaces of LaSrMnO (LSMO) thin
films grown on SrTiO (001) substrates by laser molecular beam epitaxy,
and investigated the electronic structure near the Fermi level (). The
experimental results were compared with the band-structure calculation based on
LDA + . The band structure of LSMO thin films consists of several highly
dispersive O 2 derived bands in the binding energy range of 2.0 - 6.0 eV and
Mn 3 derived bands near . ARPES spectra around the point show
a dispersive band near indicative of an electron pocket centered at the
point, although it was not so clearly resolved as an electronlike
pocket due to the suppression of spectral weight in the vicinity of .
Compared with the band-structure calculation, the observed conduction band is
assigned to the Mn 3 majority-spin band responsible for the
half-metallic nature of LSMO. We have found that the estimated size of the
Fermi surface is consistent with the prediction of the band-structure
calculation, while the band width becomes significantly narrower than the
calculation. Also, the intensity near is strongly reduced. The origin
of these discrepancies between the experiment and the calculation is discussed.Comment: 7 pages, 5 figure
Angle-resolved photoemission spectroscopy of perovskite-type transition-metal oxides and their analyses using tight-binding band structure
Nowadays it has become feasible to perform angle-resolved photoemission
spectroscopy (ARPES) measurements of transition-metal oxides with
three-dimensional perovskite structures owing to the availability of
high-quality single crystals of bulk and epitaxial thin films. In this article,
we review recent experimental results and interpretation of ARPES data using
empirical tight-binding band-structure calculations. Results are presented for
SrVO (SVO) bulk single crystals, and LaSrFeO (LSFO) and
LaSrMnO (LSMO) thin films. In the case of SVO, from comparison
of the experimental results with calculated surface electronic structure, we
concluded that the obtained band dispersions reflect the bulk electronic
structure. The experimental band structures of LSFO and LSMO were analyzed
assuming the G-type antiferromagnetic state and the ferromagnetic state,
respectively. We also demonstrated that the intrinsic uncertainty of the
electron momentum perpendicular to the crystal surface is important for the
interpretation of the ARPES results of three-dimensional materials.Comment: 25 pages, 12 figure
Madelung potentials and covalency effect in strained LaSrMnO thin films studied by core-level photoemission spectroscopy
We have investigated the shifts of the core-level photoemission spectra of
LaSrMnO thin films grown on three kinds of substrates,
SrTiO, (LaAlO)-(SrAlTaO), and
LaAlO. The experimental shifts of the La 4d and Sr 3d core levels are
almost the same as the calculation, which we attribute to the absence of
covalency effects on the Madelung potentials at these atomic sites due to the
nearly ionic character of these atoms. On the other hand, the experimental
shifts of the O and Mn core levels are negligibly small, in
disagreement with the calculation. We consider that this is due to the strong
covalent character of the Mn-O bonds.Comment: 4 pages, 5 figure
Suppression of the soybean cyst nematode, Heterodera glycines, by short-term field cultivation and soil incorporation of mung bean.
© Koninklijke Brill NV, Leiden, 2021. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1163/15685411-bja10042Our previous study using pots reported that short-term growth of mung bean (Vigna radiata) may be useful to decrease the density of the soybean cyst nematode (SCN), Heterodera glycines, in soil. The objective of this study was to determine whether short-term growth of mung bean and its incorporation by ploughing decreased SCN density in infested fields. Firstly, we did pot experiments to evaluate the optimum temperature and moisture for hatching in soil. SCN hatching was stimulated at 25 and 30°C and not at 20°C; however, it was stimulated at alternating temperature conditions between 20 and 25°C. Soil moisture levels with pF 2.76 or less were required to stimulate SCN hatch in soil. Field experiments were done in Saitama, Kanagawa and Nara Prefectures, Japan. SCN density was reduced by nearly half even in control plots, in which mung bean was not cultivated and ploughed, in Saitama and Nara Prefectures. However, SCN density was reduced by nearly 80% or more in the three Prefectures, except for one plot in Kanagawa, and the soil temperature and moisture conditions were kept at around 20-30°C and at <pF 2.8. Increase in yield of green soybean by SCN control was estimated at 350 kg (1000 m)−2. Overall, the present study revealed that short-term field cultivation of mung bean and ploughing was a profitable method to decrease SCN density in infested fields and thereby to increase yield of green soybean.Peer reviewedFinal Accepted Versio
Effect of strong localization of doped holes in angle-resolved photoemission spectra of LaSrFeO
We have performed an angle-resolved photoemission spectroscopy study of
LaSrFeO using {\it in situ} prepared thin films and
determined its band structure. The experimental band dispersions could be well
explained by an empirical band structure assuming the G-type antiferromagnetic
state. However, the Fe 3d bands were found to be shifted downward relative to
the Fermi level () by eV compared with the calculation and to
form a (pseudo)gap of eV at . We attribute this observation to a
strong localization effect of doped holes due to polaron formation.Comment: 5 pages, 5 figure
Photoemission from buried interfaces in SrTiO3/LaTiO3 superlattices
We have measured photoemission spectra of SrTiO3/LaTiO3 superlattices with a
topmost SrTiO3 layer of variable thickness. Finite coherent spectral weight
with a clear Fermi cut-off was observed at chemically abrupt SrTiO3/LaTiO3
interfaces, indicating that an ``electronic reconstruction'' occurs at the
interface between the Mott insulator LaTiO3 and the band insulator SrTiO3. For
SrTiO3/LaTiO3 interfaces annealed at high temperatures (~ 1000 C), which leads
to Sr/La atomic interdiffusion and hence to the formation of La1-xSrxTiO3-like
material, the intensity of the incoherent part was found to be dramatically
reduced whereas the coherent part with a sharp Fermi cut-off is enhanced due to
the spread of charge. These important experimental features are well reproduced
by layer dynamical-mean-field-theory calculation
New Perspectives in Sinographic Language Processing Through the Use of Character Structure
Chinese characters have a complex and hierarchical graphical structure
carrying both semantic and phonetic information. We use this structure to
enhance the text model and obtain better results in standard NLP operations.
First of all, to tackle the problem of graphical variation we define
allographic classes of characters. Next, the relation of inclusion of a
subcharacter in a characters, provides us with a directed graph of allographic
classes. We provide this graph with two weights: semanticity (semantic relation
between subcharacter and character) and phoneticity (phonetic relation) and
calculate "most semantic subcharacter paths" for each character. Finally,
adding the information contained in these paths to unigrams we claim to
increase the efficiency of text mining methods. We evaluate our method on a
text classification task on two corpora (Chinese and Japanese) of a total of 18
million characters and get an improvement of 3% on an already high baseline of
89.6% precision, obtained by a linear SVM classifier. Other possible
applications and perspectives of the system are discussed.Comment: 17 pages, 5 figures, presented at CICLing 201
Valence changes associated with the metal-insulator transition in BiLaNiO
Perovskite-type BiNiO is an insulating antiferromagnet in which a charge
disproportionation occurs at the Bi site. La substitution for Bi suppresses the
charge disproportionation and makes the system metallic. We have measured the
photoemission and x-ray absorption (XAS) spectra of BiLaNiO
to investigate how the electronic structure changes with La doping. From Ni
XAS, we observed an increase of the valence of Ni from 2+ toward 3+.
Combined with the core-level photoemission study, it was found that the average
valence of Bi remains and that the Ni valence behaves as , that is, La substitution results in hole doping at the Ni sites. In
the valence-band photoemission spectra, we observed a Fermi cutoff for ,
consistent with the metallic behavior of the La-doped compounds. The Ni
XAS, Ni core-level photoemission, and valence-band photoemission spectra
were analyzed by configuration-interaction cluster-model calculation, and the
spectral line shapes were found to be consistent with the gradual Ni
Ni valence change.Comment: 6 pages, 7 figure
Ab-initio electronic and magnetic structure in La_0.66Sr_0.33MnO_3: strain and correlation effects
The effects of tetragonal strain on electronic and magnetic properties of
strontium-doped lanthanum manganite, La_{2/3}Sr_{1/3}MnO_3 (LSMO), are
investigated by means of density-functional methods. As far as the structural
properties are concerned, the comparison between theory and experiments for
LSMO strained on the most commonly used substrates, shows an overall good
agreement: the slight overestimate (at most of 1-1.5 %) for the equilibrium
out-of-plane lattice constants points to possible defects in real samples. The
inclusion of a Hubbard-like contribution on the Mn d states, according to the
so-called "LSDA+U" approach, is rather ineffective from the structural point of
view, but much more important from the electronic and magnetic point of view.
In particular, full half-metallicity, which is missed within a bare
density-functional approach, is recovered within LSDA+U, in agreement with
experiments. Moreover, the half-metallic behavior, particularly relevant for
spin-injection purposes, is independent on the chosen substrate and is achieved
for all the considered in-plane lattice constants. More generally, strain
effects are not seen to crucially affect the electronic structure: within the
considered tetragonalization range, the minority gap is only slightly (i.e. by
about 0.1-0.2 eV) affected by a tensile or compressive strain. Nevertheless, we
show that the growth on a smaller in-plane lattice constant can stabilize the
out-of-plane vs in-plane e_g orbital and significatively change their relative
occupancy. Since e_g orbitals are key quantities for the double-exchange
mechanism, strain effects are confirmed to be crucial for the resulting
magnetic coupling.Comment: 16 pages, 7 figures, to be published on J. Phys.: Condensed Matte
Robust Ti4+ states in SrTiO3 layers of La0.6Sr0.4MnO3/SrTiO3/ La0.6Sr0.4MnO3 junctions
We have investigated the interfacial electronic structure of La0.6Sr0.4MnO3
(LSMO)/ SrTiO3 (STO)/ LSMO heterojunctions utilizing the elemental selectivity
of photoemission spectroscopy. The Ti 2p core-level spectra clearly show Ti4+
states and do not exhibit any indication of Ti3+ states in TiO2 layers
irrespective of a different kind of adjacent atomic layer with different
chemical carrier concentration. This result indicates that the Ti ions in the
TiO2 atomic layers preserve their tetravalent states even in the vicinity of
the valence-mismatched interface between LSMO and STO, reflecting chemical
stability of the Ti4+ states.Comment: 12 pages, 3 figure
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