1,649 research outputs found
Persistent detwinning of iron pnictides by small magnetic fields
Our comprehensive study on EuFeAs reveals a dramatic reduction of
magnetic detwinning fields compared to other AFeAs (A = Ba, Sr, Ca)
iron pnictides by indirect magneto-elastic coupling of the Eu ions. We
find that only 0.1T are sufficient for persistent detwinning below the local
Eu ordering; above = 19K, higher fields are necessary.
Even after the field is switched off, a significant imbalance of twin domains
remains constant up to the structural and electronic phase transition (190K).
This persistent detwinning provides the unique possibility to study the low
temperature electronic in-plane anisotropy of iron pnictides without applying
any symmetrybreaking external force.Comment: accepted by Physical Review Letter
Electronic nematic correlations in the stress free tetragonal state of BaFeNiAs
We use transport and neutron scattering to study electronic, structural, and
magnetic properties of the electron-doped BaFeNiAs iron
pnictides in the external stress free detwinned state. Using a specially
designed in-situ mechanical detwinning device, we demonstrate that the in-plane
resistivity anisotropy observed in the uniaxial strained tetragonal state of
BaFeNiAs below a temperature , previously identified as
a signature of the electronic nematic phase, is also present in the stress free
tetragonal phase below (). By carrying out neutron
scattering measurements on BaFeAs and BaFeNiAs,
we argue that the resistivity anisotropy in the stress free tetragonal state of
iron pnictides arises from the magnetoelastic coupling associated with
antiferromagnetic order. These results thus indicate that the local lattice
distortion and nematic spin correlations are responsible for the resistivity
anisotropy in the tetragonal state of iron pnictides.Comment: 5 pages, 4 figure
Microwave Conductivity due to Scattering from Extended Linear Defects in d-Wave Superconductors
Recent microwave conductivity measurements of detwinned, high-purity,
slightly overdoped YBaCuO crystals reveal a linear
temperature dependence and a near-Drude lineshape for temperatures between 1
and 20 K and frequencies ranging from 1 to 75 GHz. Prior theoretical work has
shown that simple models of scattering by point defects (impurities) in d-wave
superconductors are inconsistent with these results. It has therefore been
suggested that scattering by extended defects such as twin boundary remnants,
left over from the detwinning process, may also be important. We calculate the
self-energy and microwave conductivity in the self-consistent Born
approximation (including vertex corrections) for a d-wave superconductor in the
presence of scattering from extended linear defects. We find that in the
experimentally relevant limit (), the
resulting microwave conductivity has a linear temperature dependence and a
near-Drude frequency dependence that agrees well with experiment.Comment: 13 pages, 7 figure
Uniaxial strain detwinning of CaFe2As2 and BaFe2As2: optical and transport study
TThe parent compounds of iron-arsenide superconductors, FeAs
(=Ca, Sr, Ba), undergo a tetragonal to orthorhombic structural transition at
a temperature in the range 135 to 205K depending on the
alkaline earth element. Below the free standing crystals
split into equally populated structural domains, which mask intrinsic,
in-plane, anisotropic properties of the materials. Here we demonstrate a way of
mechanically detwinning CaFeAs and BaFeAs. The
detwinning is nearly complete, as demonstrated by polarized light imaging and
synchrotron -ray measurements, and reversible, with twin pattern restored
after strain release. Electrical resistivity measurements in the twinned and
detwinned states show that resistivity, , decreases along the
orthorhombic -axis but increases along the orthorhombic -axis in
both compounds. Immediately below the ratio = 1.2 and 1.5 for Ca and Ba compounds, respectively. Contrary to
CaFeAs, BaFeAs reveals an anisotropy in the nominally
tetragonal phase, suggesting that either fluctuations play a larger role above
in BaFeAs than in CaFeAs, or that
there is a higher temperature crossover or phase transition.Comment: extended versio
Effect of uniaxial strain on the structural and magnetic phase transitions in BaFeAs
We report neutron scattering experiments probing the influence of uniaxial
strain on both the magnetic and structural order parameters in the parent iron
pnictide compound, BaFeAs. Our data show that modest strain fields
along the in-plane orthorhombic b-axis can affect significant changes in phase
behavior simultaneous to the removal of structural twinning effects. As a
result, we demonstrate in BaFeAs samples detwinned via uniaxial strain
that the in-plane C symmetry is broken by \textit{both} the structural
lattice distortion \textit{and} long-range spin ordering at temperatures far
above the nominal (strain-free), phase transition temperatures. Surprising
changes in the magnetic order parameter of this system under relatively small
strain fields also suggest the inherent presence of magnetic domains
fluctuating above the strain-free ordering temperature in this material.Comment: 4 pages, 3 figure
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