428 research outputs found
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
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 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
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
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
Cold SO_2 molecules by Stark deceleration
We produce SO_2 molecules with a centre of mass velocity near zero using a
Stark decelerator. Since the initial kinetic energy of the supersonic SO_2
molecular beam is high, and the removed kinetic energy per stage is small, 326
deceleration stages are necessary to bring SO_2 to a complete standstill,
significantly more than in other experiments. We show that in such a
decelerator possible loss due to coupling between the motional degrees of
freedom must be considered. Experimental results are compared with 3D
Monte-Carlo simulations and the quantum state selectivity of the Stark
decelerator is demonstrated.Comment: 7 pages, 5 figure
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
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