1,837 research outputs found
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
Photoemission study of TiO2/VO2 interfaces
We have measured photoemission spectra of two kinds of TiO-capped VO
thin films, namely, that with rutile-type TiO (r-TiO/VO) and that
with amorphous TiO (a-TiO/VO) capping layers. Below the
Metal-insulator transition temperature of the VO thin films, K,
metallic states were not observed for the interfaces with TiO, in contrast
with the interfaces between the band insulator SrTiO and the Mott insulator
LaTiO in spite of the fact that both TiO and SrTiO are band
insulators with electronic configurations and both VO and LaTiO
are Mott insulators with electronic configurations. We discuss possible
origins of this difference and suggest the importance of the polarity
discontinuity of the interfaces. Stronger incoherent part was observed in
r-TiO/VO than in a-TiO/VO, suggesting Ti-V atomic diffusion due
to the higher deposition temperature for r-TiO/VO.Comment: 5 pages, 6 figure
Nonmagnetic Insulating States near the Mott Transitions on Lattices with Geometrical Frustration and Implications for -(ET)Cu
We study phase diagrams of the Hubbard model on anisotropic triangular
lattices, which also represents a model for -type BEDT-TTF compounds.
In contrast with mean-field predictions, path-integral renormalization group
calculations show a universal presence of nonmagnetic insulator sandwitched by
antiferromagnetic insulator and paramagnetic metals. The nonmagnetic phase does
not show a simple translational symmetry breakings such as flux phases,
implying a genuine Mott insulator. We discuss possible relevance on the
nonmagnetic insulating phase found in -(ET)Cu.Comment: 4pages including 7 figure
Thermodynamic Geometry of black hole in the deformed Horava-Lifshitz gravity
We investigate the thermodynamic geometry and phase transition of
Kehagias-Sfetsos black hole in the deformed Horava-Lifshitz gravity with
coupling constant . The phase transition in black hole
thermodynamics is thought to be associated with the divergence of the
capacities. And the structures of these divergent points are studied. We also
find that the thermodynamic curvature produced by the Ruppeiner metric is
positive definite for all and is divergence at
corresponded to the divergent points of and . These results
suggest that the microstructure of the black hole has an effective repulsive
interaction, which is very similar to the ideal gas of fermions. These may
shine some light on the microstructure of the black hole.Comment: 5 pages, 3 figure
Simulations of Spinodal Nucleation in Systems with Elastic Interactions
Systems with long-range interactions quenched into a metastable state near
the pseudospinodal exhibit nucleation that is qualitatively different than the
classical nucleation observed near the coexistence curve. We have observed
nucleation droplets in our Langevin simulations of a two-dimensional model of
martensitic transformations and have determined that the structure of the
nucleating droplet differs from the stable martensite structure. Our results,
together with experimental measurements of the phonon dispersion curve, allow
us to predict the nature of the droplet. These results have implications for
nucleation in many solid-solid transitions and the structure of the final
state
Effects of the Dzyaloshinskii-Moriya interaction on low energy magnetic excitations in copper benzoate
We have investigated the physical effects of the Dzyaloshinskii-Moriya (DM)
interaction in copper benzoate. In the low field limit, the spin gap is found
to vary as (: an effective staggered field
induced by the external field )in agreement with the prediction of conformal
field theory, while the staggered magnetization varies as and the
correction predicted by conformal field theory is not
confirmed.The linear scaling relation between the momentum shift and the
magnetization is broken. We have determined the coupling constant of the DM
interaction and have given a complete quantitative account for the field
dependence of the spin gaps along all three principal axes, without resorting
to additional interactions like interchain coupling. A crossover to strong
applied field behavior is predicted for further experimental verification.Comment: 4 pages and 6 figures; text revised and additional information added
for fig. 3 and a slight modification for fig.
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
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