1,398 research outputs found
A two-step optimized measurement for the phase-shift
A two-step detection strategy is suggested for the precise measurement of the optical phase-shift. In the first step an unsharp, however, unbiased joint measurement of the phase and photon number is performed by heterodyning the signal field. Information coming from this step is then used for suitable squeezing of the probe mode to obtain a sharp phase distribution. Application to squeezed states leads to a phase sensitivity scaling as relative to the total number of photons impinged into the apparatus. Numerical simulations of the whole detection strategy are also also presented
Effect of external pressure on the magnetic properties of CoAsO ( = La, Pr, Sm): a SR study
We report on a detailed investigation of the itinerant ferromagnets LaCoAsO,
PrCoAsO and SmCoAsO performed by means of muon spin spectroscopy upon the
application of external hydrostatic pressures up to GPa. These
materials are shown to be magnetically hard in view of the weak dependence of
both critical temperatures and internal fields at the muon site on .
In the cases = La and Sm, the behaviour of the internal field is
substantially unaltered up to GPa. A much richer phenomenology is
detected in PrCoAsO instead, possibly associated with a strong dependence
of the statistical population of the two different crystallographic sites for
the muon. Surprisingly, results are notably different from what is observed in
the case of the isostructural compounds CoPO, where the full As/P
substitution is already inducing a strong chemical pressure within the lattice
but is still very effective in further affecting the magnetic properties.Comment: 8 pages, 9 figure
Singling out the effect of quenched disorder in the phase diagram of cuprates
We investigate the specific influence of structural disorder on the
suppression of antiferromagnetic order and on the emergence of cuprate
superconductivity. We single out pure disorder, by focusing on a series of
YEuBaCuO samples at fixed oxygen content
, in the range . The gradual Y/Eu isovalent substitution
smoothly drives the system through the Mott-insulator to superconductor
transition from a full antiferromagnet with N\'eel transition K at
to a bulk superconductor with superconducting critical temperature
K at , YBaCuO. The electronic properties are
finely tuned by gradual lattice deformations induced by the different cationic
radii of the two lanthanides, inducing a continuous change of the basal Cu(1)-O
chain length, as well as a controlled amount of disorder in the active
Cu(2)O bilayers. We check that internal charge transfer from the basal to
the active plane is entirely responsible for the doping of the latter and we
show that superconductivity emerges with orthorhombicity. By comparing
transition temperatures with those of the isoelectronic clean system we
deterime the influence of pure structural disorder connected with the Y/Eu
alloy.Comment: 10 pages 11 figures, submitted to Journal of Physics: Condensed
Matter, Special Issue in memory of Prof. Sandro Massid
Evidence of orbital reconstruction at interfaces in La0.67Sr0.33MnO3 films
Electronic properties of transition metal oxides at interfaces are influenced
by strain, electric polarization and oxygen diffusion. Linear dichroism (LD)
x-ray absorption, diffraction, transport and magnetization on thin
La0.7Sr0.3MnO3 films, allow identification of a peculiar universal interface
effect. We report the LD signature of preferential 3d-eg(3z2-r2) occupation at
the interface, suppressing the double exchange mechanism. This surface orbital
reconstruction is opposite of that favored by residual strain and independent
of dipolar fields, chemical nature of the substrate and capping.Comment: 13 pages, 5 figure
Nanoscopic coexistence of magnetic and superconducting states within the FeAs layers of CeFeAsO1-xFx
We report on the coexistence of magnetic and superconducting states in
CeFeAsO1-xFx for x=0.06(2), characterized by transition temperatures T_m=30 K
and T_c=18 K, respectively. Zero and transverse field muon-spin relaxation
measurements show that below 10 K the two phases coexist within a nanoscopic
scale over a large volume fraction. This result clarifies the nature of the
magnetic-to-superconducting transition in the CeFeAsO1-xFx phase diagram, by
ruling out the presence of a quantum critical point which was suggested by
earlier studies.Comment: 4 pages, 3 figs, accepted for publication as PRB Rapid com
Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by Muon Spin Rotation
We have studied by muon spin resonance ({\mu}SR) the helical ground state and
fluctuating chiral phase recently observed in the MnGe chiral magnet. At low
temperature, the muon polarization shows double period oscillations at short
time scales. Their analysis, akin to that recently developed for MnSi [A. Amato
et al., Phys. Rev. B 89, 184425 (2014)], provides an estimation of the field
distribution induced by the Mn helical order at the muon site. The refined muon
position agrees nicely with ab initio calculations. With increasing
temperature, an inhomogeneous fluctuating chiral phase sets in, characterized
by two well separated frequency ranges which coexist in the sample. Rapid and
slow fluctuations, respectively associated with short range and long range
ordered helices, coexist in a large temperature range below T = 170 K. We
discuss the results with respect to MnSi, taking the short helical period,
metastable quenched state and peculiar band structure of MnGe into account.Comment: 13 pages, 11 figure
Common effect of chemical and external pressures on the magnetic properties of RECoPO (RE = La, Pr)
We report a detailed investigation of RECoPO (RE = La, Pr) and LaCoAsO
materials performed by means of muon spin spectroscopy. Zero-field measurements
show that the electrons localized on the Pr ions do not play any role in
the static magnetic properties of the compounds. Magnetism at the local level
is indeed fully dominated by the weakly-itinerant ferromagnetism from the Co
sublattice only. The increase of the chemical pressure triggered by the
different ionic radii of La and Pr, on the other hand, plays a
crucial role in enhancing the value of the magnetic critical temperature and
can be mimicked by the application of external hydrostatic pressure up to 24
kbar. A sharp discontinuity in the local magnetic field at the muon site in
LaCoPO at around 5 kbar suggests a sizeable modification in the band structure
of the material upon increasing pressure. This scenario is qualitatively
supported by \emph{ab-initio} density-functional theory calculations.Comment: 13 pages, 10 figure
Unusual disordering processes of oxygen overlayers on Rh(111): A combined diffraction study using thermal He atoms and low-energy electrons
The temperature-dependent behavior of the Rh(111)-(2X2)-1O phase was investigated by He-atom scattering (HAS) and low-energy electron diffraction. The adsorption system undergoes an order-disorder phase transition at Tc=280±5 K, with critical exponents found to be consistent with the four-state Potts model. Beyond the phase transition the HAS specular peak intensity exhibits a strong and reversible increase. This finding points toward a reduction of the surface charge-density corrugation induced by the phase transition itself. Around 160 K, hydrogen adsorbed on the Rh(111)-(2X2)-1O surface reacts with oxygen to form water, and drives the overlayer in an out-of-equilibrium condition which is characterized by a dramatic domain-wall proliferation
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