522 research outputs found
Chemical potential shift induced by double-exchange and polaronic effects in Nd_{1-x}Sr_xMnO_3
We have studied the chemical potential shift as a function of temperature in
NdSrMnO (NSMO) by measurements of core-level photoemission
spectra. For ferromagnetic samples ( and 0.45), we observed an unusually
large upward chemical potential shift with decreasing temperature in the
low-temperature region of the ferromagnetic metallic (FM) phase. This can be
explained by the double-exchange (DE) mechanism if the band is split by
dynamical/local Jahn-Teller effect. The shift was suppressed near the Curie
temperature (), which we attribute to the crossover from the DE to
lattice-polaron regimes.Comment: 5 pages, 6 figure
Chemical potential shift and spectral weight transfer in PrCaMnO revealed by photoemission spectroscopy
We have studied the chemical potential shift and changes in the electronic
density of states near the Fermi level () as a function of carrier
concentration in PrCaMnO (PCMO, ) through
the measurements of photoemission spectra. The results showed that the chemical
potential shift was suppressed for x \agt 0.3, where the charge exchange
(CE)-type antiferromagnetic charge-ordered state appears at low temperatures.
We consider this observation to be related to charge self-organization such as
stripe formation on a microscopic scale in this composition range. Together
with the previous observation of monotonous chemical potential shift in
LaSrMnO, we conclude that the tendency toward the charge
self-organization increases with decreasing bandwidth. In the valence band,
spectral weight of the Mn 3 electrons in PCMO was transferred from
1 eV below to the region near with hole doping, leading to a
finite intensity at even in the paramagnetic insulating phase for x \agt
0.3, probably related with the tendency toward charge self-organization. The
finite intensity at in spite of the insulating transport behavior is
consistent with fluctuations involving ferromagnetic metallic states.Comment: 6 pages, 5 figure
Chemical potential landscape in band filling and bandwidth-control of manganites: Photoemission spectroscopy measurements
We have studied the effects of band filling and bandwidth control on the
chemical potential in perovskite manganites MnO ( : rare
earth, : alkaline earth) by measurements of core-level photoemission
spectra. A suppression of the doping-dependent chemical potential shift was
observed in and around the CE-type charge-ordered composition range, indicating
that there is charge self-organization such as stripe formation or its
fluctuations. As a function of bandwidth, we observed a downward chemical
potential shift with increasing bandwidth due to the reduction of the
orthorhombic distortion. After subtracting the latter contribution, we found an
upward chemical potential shift in the ferromagnetic metallic region
, which we attribute to the enhancement of double-exchange
interaction involving the Jahn-Teller-split band.Comment: 5 pages, 4 figure
Theoretical demonstration of highly efficient cw THz generation by using composite photonic-structure elements
We theoretically propose one-dimensional composite photonic structures for high-resolution THz spectroanalysis. We compare the performance of two GaAs/AlAs composite photonic-structure devices, one with usual 1/4-wavelength layers of distributed Bragg reflectors (DBRs), and the other with the designed DBRs. The device with designed DBRs shows the optical-to-terahertz conversion efficiency up to 10^-5 and wide frequency tunability ranging from sub-THz to 3 THz. We found that the composite photonic structure allows us to control photonic modes with a high degree of freedom by flexible structure designs. This device achieve a cw THz source with a highly narrow bandwidth operating at room temperature
Linear Responses in Time-dependent Hartree-Fock-Bogoliubov Method with Gogny Interaction
A numerical method to integrate the time-dependent Hartree-Fock Bogoliubov
(TDHFB) equations with Gogny interaction is proposed. The feasibility of the
TDHFB code is illustrated by the conservation of the energy, particle numbers,
and center-of-mass in the small amplitude vibrations of oxygen 20. The TDHFB
code is applied to the isoscalar quadrupole and/or isovector dipole vibrations
in the linear (small amplitude) region in oxygen isotopes (masses A = 18,20,22
and 24), titanium isotopes (A = 44,50,52 and 54), neon isotope (A = 26), and
magnesium isotopes (A = 24 and 34). The isoscalar quadrupole and isovector
dipole strength functions are calculated from the expectation values of the
isoscalar quadrupole and isovector dipole moments.Comment: 10 pages, 13 figure
Representation of Neck Velocity and Neck–Vestibular Interactions in Pursuit Neurons in the Simian Frontal Eye Fields
The smooth pursuit system must interact with the vestibular system to maintain the accuracy of eye movements in space (i.e., gaze-movement) during head movement. Normally, the head moves on the stationary trunk. Vestibular signals cannot distinguish whether the head or whole body is moving. Neck proprioceptive inputs provide information about head movements relative to the trunk. Previous studies have shown that the majority of pursuit neurons in the frontal eye fields (FEF) carry visual information about target velocity, vestibular information about whole-body movements, and signal eye- or gaze-velocity. However, it is unknown whether FEF neurons carry neck proprioceptive signals. By passive trunk-on-head rotation, we tested neck inputs to FEF pursuit neurons in 2 monkeys. The majority of FEF pursuit neurons tested that had horizontal preferred directions (87%) responded to horizontal trunk-on-head rotation. The modulation consisted predominantly of velocity components. Discharge modulation during pursuit and trunk-on-head rotation added linearly. During passive head-on-trunk rotation, modulation to vestibular and neck inputs also added linearly in most neurons, although in half of gaze-velocity neurons neck responses were strongly influenced by the context of neck rotation. Our results suggest that neck inputs could contribute to representing eye- and gaze-velocity FEF signals in trunk coordinates
Electronic Structure of Noncentrosymmetric Superconductor Li(PdPt3)B Studied by Photoemission Spectroscopy
We have performed x-ray photoemission spectroscopy on the system of
noncentrosymmetric superconductor, Li(PdPt3)B. For
LiPtB, we found 2 major peaks with 2 other weak components, and the
band calculations were in agreement with the observation. The assignment of
valence band features using the calculated partial density of states determined
that Pt 5d and B 2p contribute to the density of states at the Fermi level. The
effect of antisymmetric spin-orbit coupling on the band structure might have
been probed, and the analysis on the effect of Pt incorporation into the system
indicates the smooth evolution of electronic structures. We presented the
measurements of core levels (Pd 3d, Pt 4f, and B 1s) and discussed the chemical
bonding states and electronic structures from them.Comment: 14 pages, 5 figure
COVID-19 and undeclared work: impacts and policy responses in Europe
The Coronavirus pandemic has led to restrictions on movement and workplace closures, resulting in governments offering temporary financial support to enterprises and workers. This paper evaluates a group unable to access this financial support, namely those in the undeclared economy, and possible policy responses. To identify the service industries and workers involved, a late 2019 Eurobarometer survey of undeclared work in Europe is reported. This reveals that undeclared work is particularly prevalent in the hospitality, retail and personal services sectors and identifies the population groups over-represented. Given that this undeclared workforce is now largely unable to work, it will be argued that providing access to temporary financial support, through a voluntary disclosure initiative, would be a useful initiative not only to provide the income support these enterprises and workers need but also to bring them out of the shadows and put them on the radar of the state authorities
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