374 research outputs found

    Role of Orbital Degeneracy in Double Exchange Systems

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    We investigate the role of orbital degeneracy in the double exchange (DE) model. In the JH→∞J_{H}\to\infty limit, an effective generalized ``Hubbard'' model incorporating orbital pseudospin degrees of freedom is derived. The model possesses an exact solution in one- and in infinite dimensions. In 1D, the metallic phase off ``half-filling'' is a Luttinger liquid with pseudospin-charge separation. Using the d=∞d=\infty solution for our effective model, we show how many experimental observations for the well-doped (x≃0.3x\simeq 0.3) three-dimensional manganites La1−xSrxMnO3La_{1-x}Sr_{x}MnO_{3} can be qualitatively explained by invoking the role of orbital degeneracy in the DE model.Comment: 8 pages, 2 figures, submitted to Phys. Rev.

    Transition between two ferromagnetic states driven by orbital ordering in La_{0.88}Sr_{0.12}MnO_3

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    A lightly doped perovskite mangantite La_{0.88}Sr_{0.12}MnO_3 exhibits a phase transition at T_{OO}=145 K from a ferromagnetic metal (T_C=172 K) to a novel ferromagnetic insulator.We identify that the key parameter in the transition is the orbital degree of freedom in e_g electrons. By utilizing the resonant x-ray scattering technique, orbital ordering is directly detected below T_{OO}, in spite of a significant diminution of the cooperative Jahn-Teller distortion. The new experimental features are well described by a theory treating the orbital degree of freedom under strong electron correlation. The present experimental and theoretical studies uncover a crucial role of the orbital degree in the metal-insulator transition in lightly doped manganites.Comment: 4 pages, 4 figure

    Phase Transition in Perovskite Manganites with Orbital Degree of Freedom

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    Roles of orbital degree of freedom of Mn ions in phase transition as a function of temperature and hole concentration in perovskite manganites are studied. It is shown that the orbital order-disorder transition is of the first order in the wide region of hole concentration and the Neˊ\rm \acute{e}el temperature for the anisotropic spin ordering, such as the layer-type antiferromagnetic one, is lower than the orbital ordering temperature due to the anisotropy in the orbital space. The calculated results of the temperature dependence of the spin and orbital order parameters explain a variety of the experiments observed in manganites.Comment: 10 pages, 5 figure

    Strain effect on electronic transport and ferromagnetic transition temperature in La0.9_{0.9}Sr0.1_{0.1}MnO3_{3} thin films

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    We report on a systematic study of strain effects on the transport properties and the ferromagnetic transition temperature TcT_{c} of high-quality La0.9_{0.9}Sr0.1_{0.1}MnO3_{3} thin films epitaxially grown on (100) SrTiO3_{3} substrates. Both the magnetization and the resistivity are critically dependent on the film thickness. TcT_{c} is enhanced with decreasing the film thickness due to the compressive stain produced by lattice mismatch. The resistivity above 165 K of the films with various thicknesses is consistent with small polaronic hopping conductivity. The polaronic formation energy EPE_{P} is reduced with the decrease of film thickness. We found that the strain dependence of TcT_{c} mainly results from the strain-induced electron-phonon coupling. The strain effect on EPE_{P} is in good agreement with the theoretical predictions.Comment: 6 pages and 5 figures, accepted for publication in Phys. Rev.

    State owned enterprises as bribe payers: the role of institutional environment

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    Our paper draws attention to a neglected channel of corruption—the bribe payments by state-owned enterprises (SOEs). This is an important phenomenon as bribe payments by SOEs fruitlessly waste national resources, compromising public welfare and national prosperity. Using a large dataset of 30,249 firms from 50 countries, we show that, in general, SOEs are less likely to pay bribes for achieving organizational objectives owing to their political connectivity. However, in deteriorated institutional environments, SOEs may be subjected to potential managerial rent-seeking behaviors, which disproportionately increase SOE bribe propensity relative to privately owned enterprises. Specifically, our findings highlight the importance of fostering democracy and rule of law, reducing prevalence of corruption and shortening power distance in reducing the incidence of SOE bribery

    Technological Pathways to Produce Compressed and Highly Pure Hydrogen from Solar Power

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    Hydrogen H2 produced from renewables will have a growing impact on the global energy dynamics towards sustainable and carbon neutral standards. The share of green H2 is still too low to meet the net zero target, while the demand for high quality hydrogen continues to rise. These factors amplify the need for economically viable H2 generation technologies. The present article aims at evaluating the existing technologies for high quality H2 production based on solar energy. Technologies such as water electrolysis, photoelectrochemical and solar thermochemical water splitting, liquid metal reactors and plasma conversion utilize solar power directly or indirectly as carbon neutral electrons and are reviewed from the perspective of their current development level, technical limitations and future potentia

    Corruption and its effects on FDI:Analysing the interaction between the corruption levels of the home and host countries and its effects at the decision-making level

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    This study furthers our understanding of how corruption affects the decision-making process of allocating foreign direct investment. Drawing on the responses of 28 managers in charge of establishing operations in a highly corrupt host country, we argue that those firms based in home countries with low levels of corruption are more proactive in preparing to face corruption abroad than those based in countries with high corruption levels. This means that firms from less corrupt home countries have strategies in place to deal with high corruption abroad. This finding is based on the fact that these firms have stronger pressures to not engage in corruption from their home stakeholders. Also, these firms might not have the experience of dealing with corruption at home, which hinders their potential to deal with corruption abroad. On the other hand, those firms based in highly corrupt home countries do not have clear strategies to deal with corruption abroad. This assertion is based on the fact that these firms might have familiarity in dealing with corruption and thus, might not see it as an obstacle to operating abroad
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