Band-width control in a perovskite-type 3d^1 correlated metal Ca_1-xSr_xVO_3. II. Optical spectroscopy investigation

Optical conductivity spectra of single crystals of Ca_1-xSr_xVO_3 have been studied to elucidate how the electronic behavior depends on the strength of the electron correlation without changing the nominal number of electrons per vanadium atom. The effective mass deduced by the analysis of the Drude-like contribution do not show critical enhancement, even though the system is close to the Mott transition. Besides the Drude-like contribution, two anomalous features were observed in the optical conductivity spectra of the intraband transition within the 3d band. These features can be assigned to transitions involving the incoherent and coherent bands near the Fermi level. The large spectral weight redistribution in this system, however, does not involve a large mass enhancement.Comment: 12 pages in a Phys. Rev. B camera-ready format with 16 EPS figures embedded. LaTeX 2.09 source file using "camera.sty" and "prbplug.sty" provided by N. Shirakawa. For OzTeX (Macintosh), use "ozfig.sty" instead of "psfig.sty". "ozfig.sty" can be also obtained by e-mail request to N. Shirakawa: . Submitted to Phys. Rev. B. See "Part I (by Inoue et al.)" at cond-mat/980107

Magnetooptical sum rules close to the Mott transition

We derive new sum rules for the real and imaginary parts of the frequency-dependent Hall constant and Hall conductivity. As an example, we discuss their relevance to the doped Mott insulator that we describe within the dynamical mean-field theory of strongly correlated electron systems.Comment: 4 pages, 4 ps figures; accepted for publication in PR

Photoemission Quasi-Particle Spectra of Sr2_2RuO4_4

Multi-band quasi-particle calculations based on perturbation theory and dynamical mean field methods show that the creation of a photoemission hole state in Sr$_2$RuO$_4$ is associated with a highly anisotropic self-energy. Since the narrow Ru-derived $d_{xz,yz}$ bands are more strongly distorted by Coulomb correlations than the wide $d_{xy}$ band, charge is partially transferred from $d_{xz,yz}$ to $d_{xy}$, thereby shifting the $d_{xy}$ van Hove singularity close to the Fermi level.Comment: 4 pages, to be published in PRB Rapid Com

Surface metal-insulator transition in the Hubbard model

The correlation-driven metal-insulator (Mott) transition at a solid surface is studied within the Hubbard model for a semi-infinite lattice by means of the dynamical mean-field theory. The transition takes place at a unique critical strength of the interaction. Depending on the surface geometry, the interaction strength and the wave vector, we find one-electron excitations in the coherent part of the surface-projected metallic spectrum which are confined to two dimensions.Comment: LaTeX, 9 pages, 5 eps figures included, Phys. Rev. B (in press

Spectral evolution in (Ca,Sr)RuO_3 near the Mott-Hubbard transition

We investigated the optical properties of (Ca,Sr)RuO_3 films on the borderline of a metal-insulator (M-I) transition. Our results show all of the predicted characteristics for a metallic Mott-Hubbard system, including (i) a mass enhancement in dc-limit, (ii) an U/2 excitation, and (iii) an U excitation. Also, a self-consistency is found within the Gutzwiller-Brinkman-Rice picture for the Mott transition. Our finding displays that electron correlation should be important even in 4d materials.Comment: REVTEX 4 pages, 5 EPS figures, submitted to Phys. Rev. Let

k-dependent spectrum and optical conductivity near metal-insulator transition in multi-orbital Hubbard bands

We apply the dynamical mean field theory (DMFT) in the iterative perturbation theory(IPT) to doubly degenerate eg bands and triply degenerate tg bands on a simple cubic lattice and calculate the spectrum and optical conductivity in arbitrary electron occupation. The spectrum simultaneously shows the effects of multiplet structure and DMFT together with the electron ionization and affinity levels of different electron occupations, coherent peaks at the Fermi energy in the metallic phase and a gap at an integer filling of electrons for sufficiently large Coulomb U. We also calculate the critical value of the Coulomb U for degenerate orbitals.Comment: 8 pages, 6 figure

Topological Aspects of Gauge Fixing Yang-Mills Theory on S4

For an $S_4$ space-time manifold global aspects of gauge-fixing are investigated using the relation to Topological Quantum Field Theory on the gauge group. The partition function of this TQFT is shown to compute the regularized Euler character of a suitably defined space of gauge transformations. Topological properties of the space of solutions to a covariant gauge conditon on the orbit of a particular instanton are found using the $SO(5)$ isometry group of the $S_4$ base manifold. We obtain that the Euler character of this space differs from that of an orbit in the topologically trivial sector. This result implies that an orbit with Pontryagin number \k=\pm1 in covariant gauges on $S_4$ contributes to physical correlation functions with a different multiplicity factor due to the Gribov copies, than an orbit in the trivial \k=0 sector. Similar topological arguments show that there is no contribution from the topologically trivial sector to physical correlation functions in gauges defined by a nondegenerate background connection. We discuss possible physical implications of the global gauge dependence of Yang-Mills theory.Comment: 13 pages, uuencoded and compressed LaTeX file, no figure

A Quantum Monte Carlo Method and Its Applications to Multi-Orbital Hubbard Models

We present a framework of an auxiliary field quantum Monte Carlo (QMC) method for multi-orbital Hubbard models. Our formulation can be applied to a Hamiltonian which includes terms for on-site Coulomb interaction for both intra- and inter-orbitals, intra-site exchange interaction and energy differences between orbitals. Based on our framework, we point out possible ways to investigate various phase transitions such as metal-insulator, magnetic and orbital order-disorder transitions without the minus sign problem. As an application, a two-band model is investigated by the projection QMC method and the ground state properties of this model are presented.Comment: 10 pages LaTeX including 2 PS figures, to appear in J.Phys.Soc.Jp

Magnetic Order in the Double Exchange Model in Infinite Dimensions

We studied magnetic properties of the double exchange (DE) model with S=1/2 localized spins at T=0, using exact diagonalization in the framework of the dynamical mean field theory. Obtained phase diagram contains ferromagnetic, antiferromagnetic and paramagnetic phases. Comparing the phase diagram with that of the DE model with classical localized spins, we found that the quantum fluctuations of localized spins partly destabilize the ferromagnetism and expand the paramagnetic phase region. We found that phase separations occur between the antiferromagnetic and paramagnetic phases as well as the paramagnetic and ferromagnetic ones.Comment: 11 pages, LaTeX, 9 eps-figure

Transport of Dust Particles in Tokamak Devices

Recent advances in the dust transport modeling in tokamak devices are discussed. Topics include: (1) physical model for dust transport; (2) modeling results on dynamics of dust particles in plasma; (3) conditions necessary for particle growth in plasma; (4) dust spreading over the tokamak; (5) density profiles for dust particles and impurity atoms associated with dust ablation in tokamak plasma; and (6) roles of dust in material/tritium migration