1,477 research outputs found
Superconductivity in S-substituted FeTe
We have successfully synthesized a new superconducting phase of FeTe1-xSx
with a PbO-type structure. It has the simplest crystal structure in iron-based
superconductors. Superconducting transition temperature is about 10 K at x =
0.2. The upper critical field Hc2 was estimated to be ~70 T. The coherent
length was calculated to be ~2.2 nm. Because FeTe1-xSx is composed of nontoxic
elements, this material is a candidate for applications and will activate more
and more research on iron-based superconductor.Comment: 13 pages, 10 figure
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
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
Multiple Broken Symmetries in Striped LaBaCuO detected by the Field Symmetric Nernst Effect
We report on a thermoelectric investigation of the stripe and superconducting
phases of the cuprate LaBaCuO near the doping known
to host stable stripes. We use the doping and magnetic field dependence of
field-symmetric Nernst effect features to delineate the phenomenology of these
phases. Our measurements are consistent with prior reports of time-reversal
symmetry breaking signatures above the superconducting , and
crucially detect a sharp, robust, field-invariant peak at the stripe charge
order temperature, . Our observations
suggest the onset of a nontrivial charge ordered phase at , and the subsequent presence of spontaneously
generated vortices over a broad temperature range before the emergence of bulk
superconductivity in LBCO
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.
Commensurate-Incommensurate transition in the melting process of the orbital ordering in Pr0.5Ca0.5MnO3: neutron diffraction study
The melting process of the orbital order in
Pr0.5Ca0.5MnO3 single crystal has been studied in detail as a function of
temperature by neutron diffraction. It is demonstrated that a
commensurate-incommensurate (C-IC) transition of the orbital ordering takes
place in a bulk sample, being consistent with the electron diffraction studies.
The lattice structure and the transport properties go through drastic changes
in the IC orbital ordering phase below the charge/orbital ordering temperature
Tco/oo, indicating that the anomalies are intimately related to the partial
disordering of the orbital order, unlike the consensus that it is related to
the charge disordering process. For the same T range, partial disorder of the
orbital ordering turns on the ferromagnetic spin fluctuations which were
observed in a previous neutron scattering study.Comment: 5 pages, 2 figures, REVTeX, to be published in Phys. Rev.
Spin excitations used to probe the nature of the exchange coupling in the magnetically ordered ground state of PrCaMnO
We have used time-of-flight inelastic neutron scattering to measure the spin
wave spectrum of the canonical half-doped manganite
PrCaMnO, in its magnetic and orbitally ordered phase. The
data, which cover multiple Brillouin zones and the entire energy range of the
excitations, are compared with several different models that are all consistent
with the CE-type magnetic order, but arise through different exchange coupling
schemes. The Goodenough model, i.e. an ordered state comprising strong nearest
neighbor ferromagnetic interactions along zig-zag chains with antiferromagnetic
inter-chain coupling, provides the best description of the data, provided that
further neighbor interactions along the chains are included. We are able to
rule out a coupling scheme involving formation of strongly bound ferromagnetic
dimers, i.e. Zener polarons, on the basis of gross features of the observed
spin wave spectrum. A model with weaker dimerization reproduces the observed
dispersion but can be ruled out on the basis of discrepancies between the
calculated and observed structure factors at certain positions in reciprocal
space. Adding further neighbor interactions results in almost no dimerization,
i.e. recovery of the Goodenough model. These results are consistent with
theoretical analysis of the degenerate double exchange model for half-doping,
and provide a recipe for how to interpret future measurements away from
half-doping, where degenerate double exchange models predict more complex
ground states.Comment: 14 pages, 11 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
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