285 research outputs found

    The band structure and Fermi surface of La0.6_{0.6}Sr0.4_{0.4}MnO3_{3} thin films studied by in-situ angle-resolved photoemission spectroscopy

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    We have performed an in situ angle-resolved photoemission spectroscopy (ARPES) on single-crystal surfaces of La0.6_{0.6}Sr0.4_{0.4}MnO3_{3} (LSMO) thin films grown on SrTiO3_{3} (001) substrates by laser molecular beam epitaxy, and investigated the electronic structure near the Fermi level (EFE_{F}). The experimental results were compared with the band-structure calculation based on LDA + UU. The band structure of LSMO thin films consists of several highly dispersive O 2pp derived bands in the binding energy range of 2.0 - 6.0 eV and Mn 3dd derived bands near EFE_{F}. ARPES spectra around the GammaGamma point show a dispersive band near EFE_{F} indicative of an electron pocket centered at the GammaGamma point, although it was not so clearly resolved as an electronlike pocket due to the suppression of spectral weight in the vicinity of EFE_{F}. Compared with the band-structure calculation, the observed conduction band is assigned to the Mn 3degde_{g} 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 EFE_{F} 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

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    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 SrVO3_3 (SVO) bulk single crystals, and La1−x_{1-x}Srx_xFeO3_3 (LSFO) and La1−x_{1-x}Srx_xMnO3_3 (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 La1−x_{1-x}Srx_xMnO3_3 thin films studied by core-level photoemission spectroscopy

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    We have investigated the shifts of the core-level photoemission spectra of La0.6_{0.6}Sr0.4_{0.4}MnO3_3 thin films grown on three kinds of substrates, SrTiO3_3, (LaAlO3_3)0.3_{0.3}-(SrAl0.5_{0.5}Ta0.5_{0.5}O3_3)0.7_{0.7}, and LaAlO3_3. 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 1s1s and Mn 2p2p 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.

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    © 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 La1−x_{1-x}Srx_xFeO3_3

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    We have performed an angle-resolved photoemission spectroscopy study of La0.6_{0.6}Sr0.4_{0.4}FeO3_3 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 (EFE_F) by ∼1\sim 1 eV compared with the calculation and to form a (pseudo)gap of ∼1\sim 1 eV at EFE_F. 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

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    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

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    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 Bi1−x_{1-x}Lax_xNiO3_3

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    Perovskite-type BiNiO3_3 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 Bi1−x_{1-x}Lax_{x}NiO3_{3} to investigate how the electronic structure changes with La doping. From Ni 2p2p 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 ∼4+\sim 4+ and that the Ni valence behaves as ∼(2+x)+\sim (2+x)+, that is, La substitution results in hole doping at the Ni sites. In the valence-band photoemission spectra, we observed a Fermi cutoff for x>0x>0, consistent with the metallic behavior of the La-doped compounds. The Ni 2p2p XAS, Ni 2p2p 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 Ni2+→^{2+} \to Ni3+^{3+} valence change.Comment: 6 pages, 7 figure

    Ab-initio electronic and magnetic structure in La_0.66Sr_0.33MnO_3: strain and correlation effects

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    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
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