2,300 research outputs found
Evolution of the electronic structure across the filling-control and bandwidth-control metal-insulator transitions in pyrochlore-type Ru oxides
We have performed photoemission and soft x-ray absorption studies of
pyrochlore-type Ru oxides, namely, the filling-control system
SmCaRuO and the bandwidth-control system
SmBiRuO, which show insulator-to-metal transition with
increasing Ca and Bi concentration, respectively. Core levels and the O 2
valence band in SmCaRuO show almost the same amount of
monotonous upward energy shifts with Ca concentration, which indicates that the
chemical potential is shifted downward due to hole doping. The Ru 4 band in
SmCaRuO is also shifted toward the Fermi level () with
hole doping and the density of states (DOS) at increases. The core levels
in SmBiRuO, on the other hand, do not show clear energy
shifts except for the Ru 3 core level, whose line shape change also reflects
the increase of metallic screening with Bi concentration. We observe pronounced
spectral weight transfer from the incoherent to the coherent parts of the Ru 4d
band with Bi concentration, which is expected for a bandwidth-control
Mott-Hubbard system. The increase of the DOS at is more abrupt in the
bandwidth-control SmBiRuO than in the filling-control
SmCaRuO, in accordance with a recent theoretical
prediction. Effects of charge transfer between the Bi 6 band and the Ru
4 band are also discussed.Comment: 11 pages, 6 figure
Modulation Doping of a Mott Quantum Well by a Proximate Polar Discontinuity
We present evidence for hole injection into LaAlO3/LaVO3/LaAlO3 quantum wells
near a polar surface of LaAlO3 (001). As the surface is brought in proximity to
the LaVO3 layer, an exponential drop in resistance and a decreasing positive
Seebeck coefficient is observed below a characteristic coupling length of 10-15
unit cells. We attribute this behavior to a crossover from an atomic
reconstruction of the AlO2-terminated LaAlO3 surface to an electronic
reconstruction of the vanadium valence. These results suggest a general
approach to tunable hole-doping in oxide thin film heterostructures.Comment: 16 pages, 7 figure
Orbital ordering in LaSrMnO studied by model Hartree-Fock calculation
We have investigated orbital ordering in the half-doped manganite
LaSrMnO, which displays spin, charge and orbital ordering,
by means of unrestricted Hartree-Fock calculations on the multiband -
model. From recent experiment, it has become clear that
LaSrMnO exhibits a cross-type orbital
ordering rather than the widely believed rod-type orbital
ordering. The calculation reveals that cross-type orbital
ordering results from an effect of in-plane distortion as well as from the
relatively long out-of-plane Mn-O distance. For the "Mn" site, it is
shown that the elongation along the c-axis of the MnO octahedra leads to an
anisotropic charge distribution rather than the isotropic one.Comment: 4 pages, 5 figure
Electronic charges and electric potential at LaAlO3/SrTiO3 interfaces studied by core-level photoemission spectroscopy
We studied LaAlO3/SrTiO3 interfaces for varying LaAlO3 thickness by
core-level photoemission spectroscopy. In Ti 2p spectra for conducting "n-type"
interfaces, Ti3+ signals appeared, which were absent for insulating "p-type"
interfaces. The Ti3+ signals increased with LaAlO3 thickness, but started well
below the critical thickness of 4 unit cells for metallic transport. Core-level
shifts with LaAlO3 thickness were much smaller than predicted by the polar
catastrophe model. We attribute these observations to surface
defects/adsorbates providing charges to the interface even below the critical
thickness
Evolution of the electronic structure from electron-doped to hole-doped states in the two-dimensional Mott-Hubbard system La1.17-xPbxVS3.17
The filling-controlled metal-insulator transition (MIT) in a two-dimensional
Mott-Hubbard system La1.17-xPbxVS3.17 has been studied by photoemission
spectroscopy. With Pb substitution x, chemical potential mu abruptly jumps by ~
0.07 eV between x=0.15 and 0.17, indicating that a charge gap is opened at x ~=
0.16 in agreement with the Mott insulating state of the d2 configuration. When
holes or electrons are doped into the Mott insulator of x ~= 0.16, the gap is
filled and the photoemission spectral weight at mu, rho(mu), gradually
increases in a similar way to the electronic specific heat coefficient,
although the spectral weight remains depressed around mu compared to that
expected for a normal metal, showing a pseudogap behavior in the metallic
samples. The observed behavior of varrho(mu)->0 for x->0.16 is contrasted with
the usual picture that the electron effective mass of the Fermi-liquid system
is enhanced towards the metal-insulator boundary. With increasing temperature,
the gap or the pseudogap is rapidly filled up, and the spectra at T=300 K
appears to be almost those of a normal metal. Near the metal-insulator
boundary, the spectra around mu are consistent with the formation of a Coulomb
gap, suggesting the influence of long-range Coulomb interaction under the
structural disorder intrinsic to this system.Comment: 8 pages, 12 figure
Coherent quasi-particles-to-incoherent hole-carriers crossover in underdoped cuprates
In underdoped cuprates, only a portion of the Fermi surface survives as Fermi
arcs due to pseudogap opening. In hole-doped LaCuO, we have deduced
the "coherence temperature" of quasi-particles on the Fermi arc above
which the broadened leading edge position in angle-integrated photoemission
spectra is shifted away from the Fermi level and the quasi-particle concept
starts to lose its meaning. is found to rapidly increase with hole
doping, an opposite behavior to the pseudogap temperature . The
superconducting dome is thus located below both and , indicating
that the superconductivity emerges out of the coherent Fermionic
quasi-particles on the Fermi arc. remains small in the underdoped
region, indicating that incoherent charge carriers originating from the Fermi
arc are responsible for the apparently metallic transport at high temperatures
Chemical potential jump between hole- and electron-doped sides of ambipolar high-Tc cuprate
In order to study an intrinsic chemical potential jump between the hole- and
electron-doped high-Tc superconductors, we have performed core-level X-ray
photoemission spectroscopy (XPS) measurements of Y0.38La0.62Ba1.74La0.26Cu3Oy
(YLBLCO), into which one can dope both holes and electrons with maintaining the
same crystal structure. Unlike the case between the hole-doped system
La_2-xSrxCuO4 and the electron-doped system Nd_2-xCexCuO4, we have estimated
the true chemical potential jump between the hole- and electron-doped YLBLCO to
be ~0.8 eV, which is much smaller than the optical gaps of 1.4-1.7 eV reported
for the parent insulating compounds. We attribute the reduced jump to the
indirect nature of the charge-excitation gap as well as to the polaronic nature
of the doped carriers.Comment: 4 pages, 3 figure
Electronic structure of InMnAs studied by photoemission spectroscopy: Comparison with GaMnAs
We have investigated the electronic structure of the -type diluted
magnetic semiconductor InMnAs by photoemission spectroscopy. The Mn
3 partial density of states is found to be basically similar to that of
GaMnAs. However, the impurity-band like states near the top of
the valence band have not been observed by angle-resolved photoemission
spectroscopy unlike GaMnAs. This difference would explain the
difference in transport, magnetic and optical properties of
InMnAs and GaMnAs. The different electronic
structures are attributed to the weaker Mn 3 - As 4 hybridization in
InMnAs than in GaMnAs.Comment: 4 pages, 3 figure
Photoemission Spectral Weight Transfer and Mass Renormalization in the Fermi-Liquid System LaSrTiO
We have performed a photoemission study of LaSrTiO near
the filling-control metal-insulator transition (MIT) as a function of hole
doping. Mass renormalization deduced from the spectral weight and the width of
the quasi-particle band around the chemical potential is compared with
that deduced from the electronic specific heat. The result implies that, near
the MIT, band narrowing occurs strongly in the vicinity of . Spectral
weight transfer occurs from the coherent to the incoherent parts upon
antiferromagnetic ordering, which we associate with the partial gap opening at
.Comment: 4 pages, 3 figure
Electronic Structure of the Chevrel-Phase Compounds SnMoSe: Photoemission Spectroscopy and Band-structure Calculations
We have studied the electronic structure of two Chevrel-phase compounds,
MoSe and SnMoSe, by combining photoemission
spectroscopy and band-structure calculations. Core-level spectra taken with
x-ray photoemission spectroscopy show systematic core-level shifts, which do
not obey a simple rigid-band model. The inverse photoemission spectra imply the
existence of an energy gap located eV above the Fermi level, which is
a characteristic feature of the electronic structure of the Chevrel compounds.
Quantitative comparison between the photoemission spectra and the
band-structure calculations have been made. While good agreement between theory
and experiment in the wide energy range was obtained as already reported in
previous studies, we found that the high density of states near the Fermi level
predicted theoretically due to the Van Hove singularity is considerably reduced
in the experimental spectra taken with higher energy resolution than in the
previous reports. Possible origins are proposed to explain this observation.Comment: 8 pages, 5 figure
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