151 research outputs found
Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In
Applying a magnetic field to a ferromagnetic NiMnIn
alloy in the martensitic state induces a structural phase transition to the
austenitic state. This is accompanied by a strain which recovers on removing
the magnetic field giving the system a magnetically superelastic character. A
further property of this alloy is that it also shows the inverse magnetocaloric
effect. The magnetic superelasticity and the inverse magnetocaloric effect in
Ni-Mn-In and their association with the first order structural transition is
studied by magnetization, strain, and neutron diffraction studies under
magnetic field.Comment: 6 pages, 8 figures. Published in the Physical Review
Distinct doping dependences of the pseudogap and superconducting gap LaSrCuO cuprate superconductors
We have performed a temperature-dependent angle-integrated photoemission
study of lightly-doped to heavily-overdoped LaSrCuO and
oxygen-doped LaCuO. We found that both the magnitude * of
the (small) pseudogap and the temperature \textit{T}* at which the pseudogap is
opened increases with decreasing hole concentration, consistent with previous
studies. On the other hand, the superconducting gap was found to
remain small for decreasing hole concentration. The results can be explained if
the superconducting gap opens only on the Fermi arc around the nodal
(0,0)-() direction while the pseudogap opens around (, 0).Comment: 4 pages, 3 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
Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In
Applying a magnetic field to a ferromagnetic NiMnIn
alloy in the martensitic state induces a structural phase transition to the
austenitic state. This is accompanied by a strain which recovers on removing
the magnetic field giving the system a magnetically superelastic character. A
further property of this alloy is that it also shows the inverse magnetocaloric
effect. The magnetic superelasticity and the inverse magnetocaloric effect in
Ni-Mn-In and their association with the first order structural transition is
studied by magnetization, strain, and neutron diffraction studies under
magnetic field.Comment: 6 pages, 8 figures. Published in the Physical Review
Effects of carbon incorporation on doping state of YBa2Cu3Oy
Effects of carbon incorporation on the doping state of YBa2Cu3Oy (Y-123) were
investigated. Quantitative carbon analysis revealed that carbon could be
introduced into Y-123 from both the precursor and the sintering gas. Nearly
carbon-free (< 200 ppm) samples were prepared from a vacuum-treated precursor
by sintered at 900 ˚C and cooling with 20 ˚C /min in flowing oxygen
gas. The lower Tc (= 88 K) and higher oxygen content (y = 6.98) strongly
suggested the overdoping state, which was supported by the temperature
dependence of resisitivity and thermoelectric power. The nuclear quadrapole
resonance spectra and the Raman scattering spectra indicated that there was
almost no oxygen defect in the Cu-O chain in these samples. On the other hand,
in the same cooling condition, the samples sintered in air stayed at optimal
doping level with Tc = 93 K, and the intentionally carbon-doped sample was in
the underdoping state. It is revealed that about 60% of incorporated carbon was
substituted for Cu at the chain site in the form of CO32+, and the rest remains
at the grain boundary as carbonate impurities. Such incorporation affected the
oxygen absorption process in Y-123. It turned out that the oxygen content in
Y-123 cannot be controlled only by the annealing temperature and the oxygen
partial pressure but also by the incorporated carbon concentration.Comment: 16pages, 9figure
Coherent quasi-particles-to-incoherent hole-carriers crossover in underdoped cuprates
In underdoped cuprates, only a portion of the Fermi surface survives as Fermi
arcs due to pseudogap opening. In hole-doped LaCuO, we have deduced
the "coherence temperature" of quasi-particles on the Fermi arc above
which the broadened leading edge position in angle-integrated photoemission
spectra is shifted away from the Fermi level and the quasi-particle concept
starts to lose its meaning. is found to rapidly increase with hole
doping, an opposite behavior to the pseudogap temperature . The
superconducting dome is thus located below both and , indicating
that the superconductivity emerges out of the coherent Fermionic
quasi-particles on the Fermi arc. remains small in the underdoped
region, indicating that incoherent charge carriers originating from the Fermi
arc are responsible for the apparently metallic transport at high temperatures
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