1,607 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
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
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
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
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
Anomalous ferromagnetic spin fluctuations in an antiferromagnetic insulator Pr_{1-x}Ca_{x}MnO_{3}
The high temperature paramagnetic state in an antiferromagnetic (AFM)
insulator Pr_{1-x}Ca_{x}MnO_{3} is characterized by the ferromagnetic (FM) spin
fluctuations with an anomalously small energy scale. The FM fluctuations show a
precipitous decrease of the intensity at the charge ordering temperature
T_{CO}, but persist below T_{CO}, and vanish at the AFM transition temperature
T_{N}. These results demonstrate the importance of the spin ordering for the
complete switching of the FM fluctuation in doped manganites.Comment: REVTeX, 5 pages, 4 figures, submitted to Phys. Rev.
- …