334 research outputs found
4He experiments can serve as a database for determining the three-nucleon force
We report on microscopic calculations for the 4He compound system in the
framework of the resonating group model employing realistic nucleon-nucleon and
three nucleon forces. The resulting scattering phase shifts are compared to
those of a comprehensive R-matrix analysis of all data in this system, which
are available in numerical form. The agreement between calculation and analysis
is in most cases very good. Adding three-nucleon forces yields in many cases
large effects. For a few cases the new agreement is striking. We relate some
differencies between calculation and analysis to specific data and discuss
neccessary experiments to clarify the situation. From the results we conclude
that the data of the 4He system might be well suited to determine the structure
of the three-nucleon force.Comment: title changed,note added, format of figures changed, appearance of
figures in black-and-white changed, Phys. Rev. C 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
Ground state of excitons and charged excitons in a quantum well
A variational calculation of the ground state of a neutral exciton and of
positively and negatively charged excitons (trions) in single quantum well is
presented. We study the dependance of the correlation energy and of the binding
energy on the well width and on the hole mass. Our results are are compared
with previous theoretical results and with avalaible experimental data.Comment: 8 pages, 5 figures presented to OECS
Quenched nematic criticality separating two superconducting domes in an iron-based superconductor under pressure
The nematic electronic state and its associated nematic critical fluctuations
have emerged as potential candidates for superconducting pairing in various
unconventional superconductors. However, in most materials their coexistence
with other magnetically-ordered phases poses significant challenges in
establishing their importance. Here, by combining chemical and hydrostatic
physical pressure in FeSeS, we provide a unique access to a
clean nematic quantum phase transition in the absence of a long-range magnetic
order. We find that in the proximity of the nematic phase transition, there is
an unusual non-Fermi liquid behavior in resistivity at high temperatures that
evolves into a Fermi liquid behaviour at the lowest temperatures. From quantum
oscillations in high magnetic fields, we trace the evolution of the Fermi
surface and electronic correlations as a function of applied pressure. We
detect experimentally a Lifshitz transition that separates two distinct
superconducting regions: one emerging from the nematic electronic phase with a
small Fermi surface and strong electronic correlations and the other one with a
large Fermi surface and weak correlations that promotes nesting and
stabilization of a magnetically-ordered phase at high pressures. The lack of
mass divergence suggests that the nematic critical fluctuations are quenched by
the strong coupling to the lattice. This establishes that superconductivity is
not enhanced at the nematic quantum phase transition in the absence of magnetic
order.Comment: 4 figures, 9 page
Transmission Electron Microscopy, High Resolution X-Ray Diffraction and Rutherford Backscattering Study of Strain Release in InGaAs/GaAs Buffer Layers
Strain release and dislocation distribution in InGaAs/GaAs double heterostructures, step-graded and linear-graded buffer layers have been studied. A higher misfit dislocation density at the inner interface between the InGaAs layer and the substrate was found in all the samples. This corresponded to a strain release of the inner ternary layers much larger than predicted by equilibrium theories. The residual parallel strain of the external layers as a function of their thickness was found to follow a curve approximately of slope -0.5, in agreement with previous investigations on single InGaAs layers. This result has been interpreted as evidence that the elastic energy per unit interface area remains constant during the epilayer growth. The presence of numerous single and multiple dislocation loops inside the substrate was attributed to the strain relaxation occurring through dislocation multiplication via Frank-Read sources activated during the growth. A comparison with InGaAs/GaAs step-graded and linear-graded heterostructures is also shown and briefly discussed.
Finally, lattice plane tilts between epilayers and substrates have been found due to the imbalance in the linear density of misfit dislocations with opposite component of the Burgers vector, bâ„eff, perpendicular to the interface
Linear magnetoresistance caused by mobility fluctuations in the n-doped Cd3As2
Cd3As2 is a candidate three-dimensional Dirac semi-metal which has
exceedingly high mobility and non-saturating linear magnetoresistance that may
be relevant for future practical applications. We report magnetotransport and
tunnel diode oscillation measurements on Cd3As2, in magnetic fields up to 65 T
and temperatures between 1.5K to 300K. We find the non-saturating linear
magnetoresistance persist up to 65T and it is likely caused by disorder effects
as it scales with the high mobility, rather than directly linked to Fermi
surface changes even when approaching the quantum limit. From the observed
quantum oscillations, we determine the bulk three-dimensional Fermi surface
having signatures of Dirac behaviour with non-trivial Berry's phase shift, very
light effective quasiparticle masses and clear deviations from the
band-structure predictions. In very high fields we also detect signatures of
large Zeeman spin-splitting (g~16).Comment: 5 pages, 3 figure
MBE grown GaAsBi/GaAs multiple quantum well structures: Structural and optical characterization
A series of GaAsBi/GaAs multiple quantum well pâiân diodes were grown by molecular beam epitaxy. Nomarski images showed evidence of sub-surface damage in each diode, with an increase in the cross-hatching associated with strain relaxation for the diodes containing more than 40 quantum wells. X-ray diffraction Ïâ2Ξ scans of the (004) reflections showed that multiple quantum well regions with clearly defined well periodicities were grown. The superlattice peaks of the diodes containing more than 40 wells were much broader than those of the other diodes. The photoluminescence spectra showed a redshift of 56 meV and an attenuation of nearly two orders of magnitude for the 54 and 63 well diodes. Calculations of the quantum confinement and strain induced band gap modifications suggest that the wells in all diodes are thinner than their intended widths and that both loss of quantum confinement and strain probably contributed to the observed redshift and attenuation in the 54 and 63 well diodes. Comparison of this data with that gathered for InGaAs/GaAs multiple quantum wells, suggests that the onset of relaxation occurs at a similar average strainâthickness product for both systems. Given the rapid band gap reduction of GaAsBi with Bi incorporation, this data suggests that GaAsBi is a promising photovoltaic material candidate
An Algebraic q-Deformed Form for Shape-Invariant Systems
A quantum deformed theory applicable to all shape-invariant bound-state
systems is introduced by defining q-deformed ladder operators. We show these
new ladder operators satisfy new q-deformed commutation relations. In this
context we construct an alternative q-deformed model that preserve the
shape-invariance property presented by primary system. q-deformed
generalizations of Morse, Scarf, and Coulomb potentials are given as examples
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