Role of Frustration and Dimensionality in the Hubbard Model on the Stacked Square Lattice: Variational Cluster Approach

Using variational cluster approach, we study influence of frustration and dimensionality on magnetic properties in the ground state of Hubbard model on a stacked square lattice in the large $U$ region (U/t=10), by changing the next-nearest-neighbor hopping, $t^{\prime}$, and the interlayer hopping, $t_{\perp}$. For small $t_{\perp}<t^{\ast}_{\perp}$ with $t^{\ast}_{\perp}/t{\approx}0.44$, antiferromagnetic long-range order appears at small $t^{\prime}<t^{\prime}_{c_{1}}$, and collinear magnetic long-range order at large $t^{\prime}>t^{\prime}_{c_{2}}$. They are separated by a paramagnetic Mott insulating state which appears in the parameter region $t^{\prime}_{c_{1}}<t^{\prime}<t^{\prime}_{c_{2}}$. For large $t_{\perp}>t^{\ast}_{\perp}$, the paramagnetic Mott insulating state disappears and a direct transition between antiferromagnetic state and collinear magnetic state occurs at $t^{\prime}=t^{\prime}_{c_{3}}$. We also find that the transition from the antiferromagnetic state to the paramagnetic Mott insulating state is of the second-order and that from the collinear magnetic state to the paramagnetic Mott insulating or the antiferromagnetic state is of the first-order.Comment: 7 pages, 6 figures, submitted to Physical Review

Electron-energy-loss function of LiTaO3 and LiNbO3 by x-ray photoemission spectroscopy: Theory and experiment

We report experimental energy-loss structures in x-ray photoemission spectra of single crystalline LiTaO3 and LiNbO3, and then compare these with theoretical electron-energy-loss functions calculated from first principles using the full-potential linearized augmented plane-wave method in the local-density approximation. The energy-loss structure of core electrons can be approximated by a sum of four components: for LiTaO3, the peaks positioned at 8.0, 13.4, 15.8, and 22.6 eV; for LiNbO3, those positioned at 7.0, 12.0, 14.5, and 21.8 eV. The momentum matrix elements between Bloch functions were evaluated to determine the electron energy-loss functions. The theoretical electron-energy-loss functions agreed fairly well with the experimental one. The experimental peaks positioned at 8.0, 13.4, and 15.8 eV for LiTaO3 and those at 7.0, 12.0, and 14.5 eV for LiNbO3 were assigned to the interband transitions from the valence band to the conduction bands. The peaks at 22.6 eV for LiTaO3 and 21.8 eV for LiNbO3 were ascribed to the electron excitation from the O 2s level to the lower conduction band

Photoelectron energy-loss functions of SrTiO3, BaTiO3, and TiO2: Theory and experiment

We compare experimental O 1s electron energy-loss structures below 30 eV of single crystalline SrTiO3 ,BaTiO3, and TiO2 with their theoretical electron energy-loss functions. The photoelectron energy-loss structuresof in situ fractured surface in ultrahigh vacuum can be approximated by a sum of four components forSrTiO3 and BaTiO3, and of three components for TiO2. Electronic structures were calculated from first principlesusing the full-potential linearized augmented plane-wave method in the local-density approximation. Themomentum matrix elements between Bloch functions were evaluated to determine the electron energy-lossfunctions. The theoretical electron energy-loss functions agree well with experimental spectra except a structureat around 20 eV of SrTiO3 and that at around 18 eV of BaTiO3. The difference of high binding energypeaks is explained from the positions of semicore states

Metal-Induced Gap States at Well Defined Alkali-Halide/Metal Interfaces

In order to search for states specific to insulator/metal interfaces, we have studied epitaxially grown interfaces with element-selective near edge X-ray absorption fine structure (NEXAFS). An extra peak is observed below the bulk edge onset for LiCl films on Cu and Ag substrates. The nature of chemical bonds as probed by X-ray photoemission spectroscopy and Auger electron spectroscopy remains unchanged, so we regard this as evidence for metal-induced gap states(MIGS) formed by the proximity to a metal, rather than local bonds at the interface. The dependence on the film thickness shows that the MIGS are as thin as one monolayer. An ab initio electronic structure calculation supports the existence of the MIGS that are strongly localized at the interface.Comment: 4 pages, 5 figures, to be published in Phys. Rev. Let

Electronic structure and electrical properties of amorphous OsO2

The valence-band spectrum of an amorphous OsO2 film deposited by glow discharge of OsO4 vapor can be predicted well with calculated electronic band structure of crystalline OsO2 from first principles using the liner-muffin-tin-orbital method with the local-density approximation. Resistivity of the amorphous OsO2 was less than 631023 V cm at 80 K, and it was almost temperature independent, but the temperature coefficient of resistivity was negative. The Hall coefficient of the amorphous OsO2 increased with temperature, and was saturated at around 220 K. Temperature dependence of the Hall mobility was proportional to T3/2, and it implies that the scattering of charged carriers by ionized atoms is dominant below 220 K

Dissolved methane distribution in surface seawater and its controlling factors in mid- and high-latitudes in the Southern Ocean

第6回極域科学シンポジウム分野横断セッション：[IB1] 海氷域における生物地球化学的研究11月17日（火）　統計数理研究所 セミナー室1（D305