1,763 research outputs found
Chemical potential shift in La(1-x)Sr(x)MnO(3): Photoemission test of the phase separation scenario
We have studied the chemical potential shift in La(1-x)Sr(x)MnO(3) as a
function of doped hole concentration by core-level x-ray photoemission. The
shift is monotonous, which means that there is no electronic phase separation
on a macroscopic scale, whereas it is consistent with the nano-meter scale
cluster formation induced by chemical disorder. Comparison of the observed
shift with the shift deduced from the electronic specific heat indicates that
hole doping in La(1-x)Sr(x)MnO(3) is well described by the rigid-band picture.
In particular no mass enhancement toward the metal-insulator boundary was
implied by the chemical potential shift, consistent with the electronic
specific heat data.Comment: 7 pages, 3 figures, to be published in Europhysics Letter
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
Temperature-dependent photoemission spectral weight transfer and chemical potential shift in PrCaMnO : Implications for charge density modulation
We have studied the temperature dependence of the photoemission spectra of
PrCaMnO (PCMO) with , 0.3 and 0.5. For and 0.5,
we observed a gap in the low-temperature CE-type charge-ordered (CO) phase and
a pseudogap with a finite intensity at the Fermi level () in the
high-temperature paramagnetic insulating (PI) phase. Within the CO phase, the
spectral intensity near gradually increased with temperature. These
observations are consistent with the results of Monte Carlo simulations on a
model including charge ordering and ferromagnetic fluctuations [H. Aliaga {\it
et al.} Phys. Rev. B {\bf 68}, 104405 (2003)]. For , on the other hand,
little temperature dependence was observed within the low-temperature
ferromagnetic insulating (FI) phase and the intensity at remained low in
the high-temperature PI phase. We attribute the difference in the temperature
dependence near between the CO and FI phases to the different correlation
lengths of orbital order between both phases. Furthermore, we observed a
chemical potential shift with temperature due to the opening of the gap in the
FI and CO phases. The doping dependent chemical potential shift was recovered
at low temperatures, corresponding to the disappearance of the doping dependent
change of the modulation wave vector. Spectral weight transfer with hole
concentration was clearly observed at high temperatures but was suppressed at
low temperatures. We attribute this observation to the fixed periodicity with
hole doping in PCMO at low temperatures.Comment: 5pages, 7figure
Potential Profiling of the Nanometer-Scale Charge Depletion Layer in n-ZnO/p-NiO Junction Using Photoemission Spectroscopy
We have performed a depth-profile analysis of an all-oxide p-n junction diode
n-ZnO/p-NiO using photoemission spectroscopy combined with Ar-ion sputtering.
Systematic core-level shifts were observed during the gradual removal of the
ZnO overlayer, and were interpreted using a simple model based on charge
conservation. Spatial profile of the potential around the interface was
deduced, including the charge-depletion width of 2.3 nm extending on the ZnO
side and the built-in potential of 0.54 eV
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
Soft x-ray magnetic circular dichroism study of weakly ferromagnetic ZnVO thin film
We performed a soft x-ray magnetic circular dichroism (XMCD) study of a
ZnVO thin film which showed small ferromagnetic moment. Field and
temperature dependences of V 2 XMCD signals indicated the coexistence of
Curie-Weiss paramagnetic, antiferromagnetic, and possibly ferromagnetic V ions,
quantitatively consistent with the magnetization measurements. We attribute the
paramagnetic signal to V ions substituting Zn sites which are somewhat
elongated along the c-axis
Phase Change Observed in Ultrathin Ba0.5Sr0.5TiO3 Films by in-situ Resonant Photoemission Spectroscopy
Epitaxial Ba0.5Sr0.5TiO3 thin films were prepared on Nb-doped SrTiO3
(100)substrates by the pulsed laser deposition technique, and were studied by
measuring the Ti 2p - 3d resonant photoemission spectra in the valence-band
region as a function of film thickness, both at room temperature and low
temperature. Our results demonstrated an abrupt variation in the spectral
structures between 2.8 nm (~7 monolayers) and 2.0 nm (~5 monolayers)
Ba0.5Sr0.5TiO3 films, suggesting that there exists a critical thickness for
phase change in the range of 2.0 nm to 2.8 nm. This may be ascribed mainly to
the intrinsic size effects.Comment: 13 pages, 4 figure
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