355 research outputs found
Signatures of quantum criticality in hole-doped and chemically pressurized EuFe_2As_2 single crystals
We study the effect of hole-doping and chemical pressure (isovalent doping)
in single crystals of KEuFeAs and
EuFe(AsP), respectively, by measurements of the
thermopower, , and electrical resistivity, . The evolution of
upon doping indicates drastic changes of the electronic configuration at
critical values and , respectively,
as the spin-density-wave transition is completely suppressed and
superconductivity (SC) emerges. For the case of chemical pressure, the
comparison with published ARPES measurements indicates a Lifshitz transition at
. The temperature dependences and
observed in the normal state above the SC transition
suggest quantum criticality in both systems.Comment: PRB accepte
Upper critical magnetic field in K0.83Fe1.83Se2 and Eu0.5K0.5Fe2As2 single crystals
The H-T phase diagrams of single crystalline electron-doped K0.83Fe1.83Se2
(KFS1), K0.8Fe2Se2 (KFS2) and hole-doped Eu0.5K0.5Fe2As2 (EKFA) have been
deduced from tunnel diode oscillator-based contactless measurements in pulsed
magnetic fields up to 57 T for the inter-plane (H//c) and in-plane (H//ab)
directions. The temperature dependence of the upper critical magnetic field
Hc2(T) relevant to EFKA is accounted for by the Pauli model including an
anisotropic Pauli paramagnetic contribution (\mu_BHp=114 T for H//ab and 86 T
for H//c). This is also the case of KFS1 and KFS2 for H//ab whereas a
significant upward curvature, accounted for by a two-gap model, is observed for
H//c. Despite the presence of antiferromagnetic lattice order within the
superconducting state of the studied compounds, no influence of magnetic
ordering on the temperature dependence of Hc2(T) is observed.Comment: 9 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1104.561
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
Recommended from our members
Thermal Neutron Radiography With the Plutonium Recycle Critical Facility.
Determination of thermodynamic functions and structural parameters of NpOââș lactate complexes
Spatially-resolved potential measurement with ion crystals
We present a method to measure potentials over an extended region using
one-dimensional ion crystals in a radio frequency (RF) ion trap. The
equilibrium spacings of the ions within the crystal allow the determination of
the external forces acting at each point. From this the overall potential, and
also potentials due to specific trap features, are calculated. The method can
be used to probe potentials near proximal objects in real time, and can be
generalized to higher dimensions.Comment: 7 pages (double spaced), 3 figure
Ultrasensitive force and displacement detection using trapped ions
The ability to detect extremely small forces is vital for a variety of
disciplines including precision spin-resonance imaging, microscopy, and tests
of fundamental physical phenomena. Current force-detection sensitivity limits
have surpassed 1 (atto ) through coupling of micro or
nanofabricated mechanical resonators to a variety of physical systems including
single-electron transistors, superconducting microwave cavities, and individual
spins. These experiments have allowed for probing studies of a variety of
phenomena, but sensitivity requirements are ever-increasing as new regimes of
physical interactions are considered. Here we show that trapped atomic ions are
exquisitely sensitive force detectors, with a measured sensitivity more than
three orders of magnitude better than existing reports. We demonstrate
detection of forces as small as 174 (yocto ), with a
sensitivity 390 using crystals of Be
ions in a Penning trap. Our technique is based on the excitation of normal
motional modes in an ion trap by externally applied electric fields, detection
via and phase-coherent Doppler velocimetry, which allows for the discrimination
of ion motion with amplitudes on the scale of nanometers. These experimental
results and extracted force-detection sensitivities in the single-ion limit
validate proposals suggesting that trapped atomic ions are capable of detecting
of forces with sensitivity approaching 1 . We anticipate that
this demonstration will be strongly motivational for the development of a new
class of deployable trapped-ion-based sensors, and will permit scientists to
access new regimes in materials science.Comment: Expanded introduction and analysis. Methods section added. Subject to
press embarg
Generation of a wave packet tailored to efficient free space excitation of a single atom
We demonstrate the generation of an optical dipole wave suitable for the
process of efficiently coupling single quanta of light and matter in free
space. We employ a parabolic mirror for the conversion of a transverse beam
mode to a focused dipole wave and show the required spatial and temporal
shaping of the mode incident onto the mirror. The results include a proof of
principle correction of the parabolic mirror's aberrations. For the application
of exciting an atom with a single photon pulse we demonstrate the creation of a
suitable temporal pulse envelope. We infer coupling strengths of 89% and
success probabilities of up to 87% for the application of exciting a single
atom for the current experimental parameters.Comment: to be published in Europ. Phys. J.
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