14,997 research outputs found
Itinerant-electron Ferromagnetism in W(Nb)O3-d
The crystal structure and the magnetic properties of the W1-xNbxO3-d,
(x<0.03) system have been investigated. In contrast to the orthorhombic
diamagnetic WO3, the material with x=0.01 is paramagnetic down to 5 K.
Introducing of 2.5 at. % of Nb into WO3 leads to a tetragonal structure and to
a weak itinerant ferromagnetic ordering below TC= 225 K. The saturation
magnetic moment at 5 K is 1.07*10-3 mB, whereas the paramagnetic effective
moment is 0.06 mB per mole. This high ratio indicates itinerant ferromagnetism
in W0.975Nb0.025O3-d.Comment: accepted to Physica
Donor binding energy and thermally activated persistent photoconductivity in high mobility (001) AlAs quantum wells
A doping series of AlAs (001) quantum wells with Si delta-modulation doping
on both sides reveals different dark and post-illumination saturation
densities, as well as temperature dependent photoconductivity. The lower dark
two-dimensional electron density saturation is explained assuming deep binding
energy of Delta_DK = 65.2 meV for Si-donors in the dark. Persistent
photoconductivity (PPC) is observed upon illumination, with higher saturation
density indicating shallow post-illumination donor binding energy. The
photoconductivity is thermally activated, with 4 K illumination requiring
post-illumination annealing to T = 30 K to saturate the PPC. Dark and
post-illumination doping efficiencies are reported.Comment: The values of binding energy changed from previous versions because
of a better understanding for the dielectric permittivity. Also, the Gamma -
X donor states are better explaine
Precision Spectroscopy of Molecular Hydrogen Ions: Towards Frequency Metrology of Particle Masses
We describe the current status of high-precision ab initio calculations of
the spectra of molecular hydrogen ions (H_2^+ and HD^+) and of two experiments
for vibrational spectroscopy. The perspectives for a comparison between theory
and experiment at a level of 1 ppb are considered.Comment: 26 pages, 13 figures, 1 table, to appear in "Precision Physics of
Simple Atomic Systems", Lecture Notes in Physics, Springer, 200
Electromechanical Reliability Testing of Three-Axial Silicon Force Sensors
This paper reports on the systematic electromechanical characterization of a
new three-axial force sensor used in dimensional metrology of micro components.
The siliconbased sensor system consists of piezoresistive mechanicalstress
transducers integrated in thin membrane hinges supporting a suspended flexible
cross structure. The mechanical behavior of the fragile micromechanical
structure isanalyzed for both static and dynamic load cases. This work
demonstrates that the silicon microstructure withstands static forces of 1.16N
applied orthogonally to the front-side of the structure. A statistical Weibull
analysis of the measured data shows that these values are significantly reduced
if the normal force is applied to the back of the sensor. Improvements of the
sensor system design for future development cycles are derived from the
measurement results.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
In-Medium Similarity Renormalization Group with Chiral Two- Plus Three-Nucleon Interactions
We use the recently proposed In-Medium Similarity Renormalization Group
(IM-SRG) to carry out a systematic study of closed-shell nuclei up to
\nuc{Ni}{56}, based on chiral two- plus three-nucleon interactions. We
analyze the capabilities of the IM-SRG by comparing our results for the
ground-state energy to Coupled Cluster calculations, as well as to quasi-exact
results from the Importance-Truncated No-Core Shell Model. Using chiral two-
plus three-nucleon Hamiltonians whose resolution scales are lowered by
free-space SRG evolution, we obtain good agreement with experimental binding
energies in \nuc{He}{4} and the closed-shell oxygen isotopes, while the
calcium and nickel isotopes are somewhat overbound.Comment: 11 pages, 7 figures, submitted to Phys. Rev.
Non-Fermi-liquid scattering rates and anomalous band dispersion in ferropnictides
Angle-resolved photoemission spectroscopy (ARPES) is used to study the band
dispersion and the quasiparticle scattering rates in two ferropnictides
systems. Our ARPES results show linear-in-energy dependent scattering rates
which are constant in a wide range of control parameter and which depend on the
orbital character of the bands. We demonstrate that the linear energy
dependence gives rise to weakly dispersing band with a strong mass enhancement
when the band maximum crosses the chemical potential. In the superconducting
phase the related small effective Fermi energy favors a
Bardeen-Cooper-Schrieffer (BCS)\,\cite{Bardeen1957}-Bose-Einstein
(BE)\,\cite{Bose1924} crossover state.Comment: 5 pages, 4 figures Supplement 4 pages, 6 figure
Experimentally exploring compressed sensing quantum tomography
In the light of the progress in quantum technologies, the task of verifying
the correct functioning of processes and obtaining accurate tomographic
information about quantum states becomes increasingly important. Compressed
sensing, a machinery derived from the theory of signal processing, has emerged
as a feasible tool to perform robust and significantly more resource-economical
quantum state tomography for intermediate-sized quantum systems. In this work,
we provide a comprehensive analysis of compressed sensing tomography in the
regime in which tomographically complete data is available with reliable
statistics from experimental observations of a multi-mode photonic
architecture. Due to the fact that the data is known with high statistical
significance, we are in a position to systematically explore the quality of
reconstruction depending on the number of employed measurement settings,
randomly selected from the complete set of data, and on different model
assumptions. We present and test a complete prescription to perform efficient
compressed sensing and are able to reliably use notions of model selection and
cross-validation to account for experimental imperfections and finite counting
statistics. Thus, we establish compressed sensing as an effective tool for
quantum state tomography, specifically suited for photonic systems.Comment: 12 pages, 5 figure
Nearest-neighbour Attraction Stabilizes Staggered Currents in the 2D Hubbard Model
Using a strong-coupling approach, we show that staggered current vorticity
does not obtain in the repulsive 2D Hubbard model for large on-site Coulomb
interactions, as in the case of the copper oxide superconductors. This trend
also persists even when nearest-neighbour repulsions are present. However,
staggered flux ordering emerges {\bf only} when attractive nearest-neighbour
Coulomb interactions are included. Such ordering opens a gap along the
direction and persists over a reasonable range of doping.Comment: 5 pages with 5 .eps files (Typos in text are corrected
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
Phase transitions in spin-orbital coupled model for pyroxene titanium oxides
We study the competing phases and the phase transition phenomena in an
effective spin-orbital coupled model derived for pyroxene titanium oxides
ATiSi2O6 (A=Na, Li). Using the mean-field-type analysis and the numerical
quantum transfer matrix method, we show that the model exhibits two different
ordered states, the spin-dimer and orbital-ferro state and the spin-ferro and
orbital-antiferro state. The transition between two phases is driven by the
relative strength of the Hund's-rule coupling to the onsite Coulomb repulsion
and/or by the external magnetic field. The ground-state phase diagram is
determined. There is a keen competition between orbital and spin degrees of
freedom in the multicritical regime, which causes large fluctuations and
significantly affects finite-temperature properties in the paramagnetic phase.Comment: 4 pages, 6 figures, proceedings submitted to SPQS200
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