430 research outputs found
High-order Dy multipole motifs observed in DyB2C2 with resonant soft x-ray Bragg diffraction
Resonant soft x-ray Bragg diffraction at the Dy M4,5 edges has been exploited
to study Dy multipole motifs in DyB2C2. Our results are explained introducing
the intra-atomic quadrupolar interaction between the core 3d and valence 4f
shell. This allows us to determine for the first time higher order multipole
moments of dysprosium electrons and to draw their precise charge density.
The Dy hexadecapole and hexacontatetrapole moment have been estimated at -20%
and +30% of the quadrupolar moment, respectively. No evidence for the lock-in
of the orbitals at T_N has been observed, in contrast to earlier suggestions.
The multipolar interaction and the structural transition cooperate along c but
they compete in the basal plane explaining the canted structure along [110].Comment: 4 pages, 3 figure
Origin of the second coherent peak in the dynamical structure factor of an asymmetric spin-ladder
Appearance of the second coherent peak in the dynamical structure factor of
an asymmetric spin ladder is suggested. The general arguments are confirmed by
the first order (with respect to the asymmetry) calculation for a spin ladder
with singlet-rung ground state. Basing on this result a new interpretation is
proposed for the inelastic neutron scattering data in the spin gap compound
CuHpCl.Comment: 11 page
Multipole tensor analysis of the resonant x-ray scattering by quadrupolar and magnetic order in DyB2C2
Resonant x-ray scattering (RXS) experiment has been performed for the (3 0
1.5) superlattice reflection in the antiferroquadrupolar and antiferromagnetic
phase of DyB2C2. Azimuthal-angle dependence of the resonance enhanced
intensities for both dipolar (E1) and quadrupolar (E2) resonant processes has
been measured precisely with polarization analysis. Every scattering channel
exhibits distinctive azimuthal dependence, differently from the symmetric
reflection at (0 0 0.5) which was studied previously. We have analyzed the
results using a theory developed by Lovesey et al., which directly connects
atomic tensors with the cross-section of RXS. The fitting results indicate that
the azimuthal dependences can be explained well by the atomic tensors up to
rank 2. Rank 3 and rank 4 tensors are reflected in the data very little. In
addition, The coupling scheme among the 4f quadrupolar moment, 5d ortitals, and
the lattice has been determined from the interference among the Thomson
scattering from the lattice distortion and the resonant scatterings of E1 and
E2 processes. It has also been established from the RXS of the (3 0 1.5)
reflection that the canting of the 4f quadrupolar moments exists up to T_Q. We
also discuss a possible wavefunction of the ground state from the point-charge
model calculation.Comment: 9 pages, 10 figure
Evidence for Octupole Order in CeLaB from Resonant X-ray Scattering
The azimuthal angle dependence observed in the resonant X-ray scattering in
phase IV of CeLaB is analyzed theoretically. It is shown
that the peculiar angle dependence observed in the E2 channel is consistent
with the Gamma_{5u}-type octupole order with principal axis along (111) and
equivalent directions. Under the assumption that the four equivalent octupole
domains are nearly equally populated in the sample, the observed angle
dependences are reproduced by calculation for both sigma-sigma' and sigma-pi'
polarizations. The calculation for various symmetries of order parameters
excludes unambiguously other order parameters than the Gamma_{5u}-type
octupole.Comment: 4 pages, 2 figures, 3 tables, in JPSJ forma
Crucial Role of Quantum Entanglement in Bulk Properties of Solids
We demonstrate that the magnetic susceptibility of strongly alternating
antiferromagnetic spin-1/2 chains is an entanglement witness. Specifically,
magnetic susceptibility of copper nitrate (CN) measured in 1963 (Berger et al.,
Phys. Rev. 132, 1057 (1963)) cannot be described without presence of
entanglement. A detailed analysis of the spin correlations in CN as obtained
from neutron scattering experiments (Xu et al., Phys. Rev. Lett. 84, 4465
(2000)) provides microscopic support for this interpretation. We present a
quantitative analysis resulting in the critical temperature of 5K in both,
completely independent, experiments below which entanglement exists.Comment: 4 pages, 2 figure
Field-induced paramagnons at the metamagnetic transition in Ca1.8Sr0.2RuO4
The magnetic excitations in Ca1.8Sr0.2RuO4 were studied across the
metamagnetic transition and as a function of temperature using inelastic
neutron scattering. At low temperature and low magnetic field the magnetic
response is dominated by a complex superposition of incommensurate
antiferromagnetic fluctuations. Upon increasing the magnetic field across the
metamagnetic ransition, paramagnon and finally well-defined magnon scattering
is induced, partially suppressing the incommensurate signals. The high-field
phase in Ca1.8Sr0.2RuO4 has, therefore, to be considered as an intrinsically
ferromagnetic state stabilized by the magnetic field
Symmetry of re-entrant tetragonal phase in Ba1-xNaxFe2As2: Magnetic versus orbital ordering mechanism
Magneto-structural phase transitions in Ba1-xAxFe2As2 (A = K, Na) materials
are discussed for both magnetically and orbitally driven mechanisms, using a
symmetry analysis formulated within the Landau theory of phase transitions.
Both mechanisms predict identical orthorhombic space-group symmetries for the
nematic and magnetic phases observed over much of the phase diagram, but they
predict different tetragonal space-group symmetries for the newly discovered
re-entrant tetragonal phase in Ba1-xNaxFe2As2 (x ~ 0.24-0.28). In a magnetic
scenario, magnetic order with moments along the c-axis, as found
experimentally, does not allow any type of orbital order, but in an orbital
scenario, we have determined two possible orbital patterns, specified by
P4/mnc1' and I4221' space groups, which do not require atomic displacements
relative to the parent I4/mmm1' symmetry and, in consequence, are
indistinguishable in conventional diffraction experiments. We demonstrate that
the three possible space groups are however, distinct in resonant X-ray Bragg
diffraction patterns created by Templeton & Templeton scattering. This provides
an experimental method of distinguishing between magnetic and orbital models
Inelastic neutron scattering in random binary alloys : an augmented space approach
Combining the augmented space representation for phonons with a generalized
version of Yonezawa-Matsubara diagrammatic technique, we have set up a
formalism to seperate the coherent and incoherent part of the total intensity
of thermal neutron scattering from disordered alloys. This is done exacly
without taking any recourse to mean-field like approximation (as done
previously). The formalism includes disorder in masses, force constants and
scattering lengths. Implementation of the formalism to realistic situations is
performed by an augmented space Block recursion which calculates entire Green
matrix and self energy matrix which in turn is needed to evaluate the coherent
and incoherent intensities. we apply the formalism to NiPd and NiPt alloys.
Numerical results on coherent and incoherent scattering cross sections are
presented along the highest symmetry directions. Finally the incoherent
intensities are compared with the CPA and also with experiments.Comment: 18 pages, 13 figure
Displacement Echoes: Classical Decay and Quantum Freeze
Motivated by neutron scattering experiments, we investigate the decay of the
fidelity with which a wave packet is reconstructed by a perfect time-reversal
operation performed after a phase space displacement. In the semiclassical
limit, we show that the decay rate is generically given by the Lyapunov
exponent of the classical dynamics. For small displacements, we additionally
show that, following a short-time Lyapunov decay, the decay freezes well above
the ergodic value because of quantum effects. Our analytical results are
corroborated by numerical simulations
Novel dynamic scaling regime in hole-doped La2CuO4
Only 3% hole doping by Li is sufficient to suppress the long-range
3-dimensional (3D) antiferromagnetic order in La2CuO4.
The spin dynamics of such a 2D spin liquid state at T << J was investigated
with measurements of the dynamic magnetic structure factor S(omega,q), using
cold neutron spectroscopy, for single crystalline La2Cu0.94Li0.06O4.
S(omega,q) peaks sharply at (pi,pi) and crosses over around 50K from omega/T
scaling to a novel low temperature regime characterized by a constant energy
scale. The possible connection to a crossover from the quantum critical to the
quantum disordered regime of the 2D antiferromagnetic spin liquid is discussed.Comment: 4 pages, 4 figure
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