1,672 research outputs found
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
Circadian Organization in Hemimetabolous Insects
The circadian system of hemimetabolous insects is reviewed in respect to the locus of the circadian clock and multioscillatory organization. Because of relatively easy access to the nervous system, the neuronal organization of the clock system in hemimetabolous insects has been studied, yielding identification of the compound eye as the major photoreceptor for entrainment and the optic lobe for the circadian clock locus. The clock site within the optic lobe is inconsistent among reported species; in cockroaches the lobula was previously thought to be a most likely clock locus but accessory medulla is recently stressed to be a clock center, while more distal part of the optic lobe including the lamina and the outer medulla area for the cricket. Identification of the clock cells needs further critical studies. Although each optic lobe clock seems functionally identical, in respect to photic entrainment and generation of the rhythm, the bilaterally paired clocks form a functional unit. They interact to produce a stable time structure within individual insects by exchanging photic and temporal information through neural pathways, in which
serotonin and pigment-dispersing factor (PDF) are involved as chemical messengers. The mutual interaction also plays an important role in seasonal adaptation of the rhythm
Ultrafast Photoinduced Formation of Metallic State in a Perovskite-type Manganite with Short Range Charge and Orbital Order
Femtosecond reflection spectroscopy was performed on a perovskite-type
manganite, Gd0.55Sr0.45MnO3, with the short-range charge and orbital order
(CO/OO). Immediately after the photoirradiation, a large increase of the
reflectivity was detected in the mid-infrared region. The optical conductivity
spectrum under photoirradiation obtained from the Kramers-Kronig analyses of
the reflectivity changes demonstrates a formation of a metallic state. This
suggests that ferromagnetic spin arrangements occur within the time resolution
(ca. 200 fs) through the double exchange interaction, resulting in an ultrafast
CO/OO to FM switching.Comment: 4 figure
Jahn-Teller effect and stability of the charge-ordered state in La1-xCaxMnO3 (0.5<x<0.9) manganites
The longitudinal ultrasonic sound velocity and attenuation, the resistivity,
and lattice parameters were studied as a function of temperature from 30 K to
300 K in La1-xCaxMnO3 (0.5<x<0.9). For all the samples, a dramatic stiffening
of the sound velocity below the charge ordering transition temperature TCO was
directly driven by distinct changes of the lattice parameters due to the
formation of long range ordering of Jahn-Teller distorted MnO6 octahedra. The
relative change of the sound velocity (DeltaV/V) below TCO depends on the Ca
concentration x and reaches the maximum at x=0.75, implying that the effective
strength of electron-lattice interaction with the Jahn-Teller distortion is the
strongest at x=0.75 and hence the charge ordered state is mostly stabilized
near x=0.75 and insensitive to the application of a magnetic field, which is
supported by the charge transport properties under high magnetic fields up to
14T.Comment: 16 pages, 5 figures, PD
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
Effects of Unilateral Compound-Eye Removal on the Photoperiodic Responses of Nymphal Development in the Cricket Modicogryllus siamensis
The cricket, Modicogryllus siamensis, shows clear photoperiodic responses at 25 degrees C in nymphal development. Under long-day conditions (LD16:8), nymphs became adults about 50 days after hatching, while under short-day conditions (LD8:16) the duration of nymphal stage extended to more than 130 days. Under constant dark conditions, two developmental patterns were observed: about 60% of crickets became adults slightly slower than under the long-day conditions, and the rest at later than 100 days after hatching, like those under the short-day conditions. When the compound eye was unilaterally removed on the 2nd day of hatching, an increase of molting and an extension of the nymphal period were observed under the long-day conditions, while under the short-day conditions, some crickets developed faster and others slower than intact crickets. These results suggest that this cricket receives photoperiodic information through the compound eye, that a pair of the compound eyes is required for a complete photoperiodic response, and that interaction between bilateral circadian clocks may be also involved in the response
Interplay of the CE-type charge ordering and the A-type spin ordering in a half-doped bilayer manganite La{1}Sr{2}Mn{2}O{7}
We demonstrate that the half-doped bilayer manganite La_{1}Sr_{2}Mn_{2}O_{7}
exhibits CE-type charge-ordered and spin-ordered states below K and below K, respectively. However, the volume
fraction of the CE-type ordering is relatively small, and the system is
dominated by the A-type spin ordering. The coexistence of the two types of
ordering is essential to understand its transport properties, and we argue that
it can be viewed as an effective phase separation between the metallic
orbital ordering and the charge-localized
orbital ordering.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Growth, transport, and magnetic properties of Pr0.67Ca0.33MnO3 thin films
We have grown Pr0.67Ca0.33MnO3 thin films on LaAlO3 using pulsed laser deposition. Below 50 K, a field induced insulator-metal transition results in changes in resistivity of at least 6 orders of magnitude. The field induced conducting state is metastable at low temperature. The temperature dependence of the resistivity exhibits considerable hysteresis in a field of 40 kOe but becomes reversible in a field of 80 kOe
Soft spin waves in the low temperature thermodynamics of Pr_{0.7}Ca_{0.3}MnO_{3}
We present a detailed magnetothermal study of Pr(0.7)Ca(0.3)MnO(3), a
perovskite manganite in which an insulator-metal transition can be driven by
magnetic field, but also by pressure, visible light, x-rays, or high currents.
We find that the field-induced transition is associated with an enormous
release of energy which accounts for its strong irreversibility. In the
ferromagnetic metallic state, specific heat and magnetization measurements
indicate a much smaller spin wave stiffness than that seen in any other
manganite, which we attribute to spin waves among the ferromagnetically ordered
Pr moments. The coupling between the Pr and Mn spins may also provide a basis
for understanding the low temperature phase diagram of this most unusual
manganite.Comment: 10 pages, LATEX, 5 PDF figures, corrected typo
Effect of Co doping on the in-plane anisotropy in the optical spectrum of underdoped Ba(Fe1-xCox)2As2
We investigated the anisotropy in the in-plane optical spectra of detwinned
Ba(Fe1-xCox)2As2. The optical conductivity spectrum of BaFe2As2 shows
appreciable anisotropy in the magnetostructural ordered phase, whereas the dc
resistivity is almost isotropic at low temperatures. Upon Co doping, the
resistivity becomes highly anisotropic, while the finite-energy intrinsic
anisotropy is suppressed. It is found that anisotropy in resistivity arises
from anisotropic impurity scattering from doped Co atoms, extrinsic in origin.
Intensity of a specific optical phonon mode is also found to show striking
anisotropy in the ordered phase. The anisotropy induced by Co impurity and that
observed in the optical phonon mode are hallmarks of the highly polarizable
electronic state in the ordered phase.Comment: 5 pages, 4 figure
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