106 research outputs found
GdRhSi: An exemplary tetragonal system for antiferromagnetic order with weak in-plane anisotropy
The anisotropy of magnetic properties commonly is introduced in textbooks
using the case of an antiferromagnetic system with Ising type anisotropy. This
model presents huge anisotropic magnetization and a pronounced metamagnetic
transition and is well-known and well-documented both, in experiments and
theory. In contrast, the case of an antiferromagnetic - system with weak
in-plane anisotropy is only poorly documented. We studied the anisotropic
magnetization of the compound GdRhSi and found that it is a perfect
model system for such a weak-anisotropy setting because the Gd ions in
GdRhSi have a pure spin moment of S=7/2 which orders in a simple AFM
structure with . We observed experimentally in a
continuous spin-flop transition and domain effects for field applied along the
- and the -direction, respectively. We applied a mean field model
for the free energy to describe our data and combine it with an Ising chain
model to account for domain effects. Our calculations reproduce the
experimental data very well. In addition, we performed magnetic X-ray
scattering and X-ray magnetic circular dichroism measurements, which confirm
the AFM propagation vector to be and indicate the absence of
polarization on the rhodium atoms
Theory of Coupled Multipole Moments Probed by X-ray Scattering in CeB
A minimal model for multipole orders in CeB shows that degeneracy of the
quadrupole order parameters and strong spin-orbit coupling lead to peculiar
temperature and magnetic-field dependences of the X-ray reflection intensity at
superlattice Bragg points. Furthermore, the intensity depends sensitively on
the surface direction. These theoretical results explain naturally recent X-ray
experiments in phases II and III of CeB. It is predicted that under weak
magnetic field perpendicular to the (111) surface, the reflection intensity
should change non-monotonically as a function of temperature.Comment: 4 pages, 5 figure
Charge density waves and Fermi surface reconstruction in the clean overdoped cuprate superconductor Tl2Ba2CuO6+δ.
Hall effect and quantum oscillation measurements on high temperature cuprate superconductors show that underdoped compositions have small Fermi surface pockets whereas when heavily overdoped, a single much larger pocket is found. The origin of this change in electronic structure has been unclear, but may be related to the high temperature superconductivity. Here we show that the clean overdoped single-layer cuprate Tl2Ba2CuO6+δ (Tl2201) displays CDW order with a remarkably long correlation length ξ ≈ 200 Å which disappears above a hole doping of pCDW ≈ 0.265. We show that the evolution of the electronic properties of Tl2201 as the doping is lowered may be explained by a Fermi surface reconstruction which accompanies the emergence of the CDW below pCDW. Our results demonstrate importance of CDW correlations in understanding the electronic properties of overdoped cuprates
Coherent X-ray Scattering from Manganite Charge and Orbital Domains
We report coherent x-ray scattering studies of charge and orbital domains in
manganite systems. The experiments were carried out on LaMnO_3 and
Pr_{0.6}Ca_{0.4}MnO_3, with the incident photon energy tuned near the Mn K
edge. At room temperature, the orbital speckle pattern of LaMnO_3 was observed
to be constant over a timescale of at least minutes, which is indicative of
static orbital domains on this timescale. For Pr_{0.6}Ca_{0.4}MnO_3, both
charge and orbital speckle patterns were observed. The observation of the
latter rules out the presence of fast orbital fluctuations, while long time
series data-- on the order of several minutes-- were suggestive of slow dynamic
behavior. In contrast, the charge order speckle patterns were static.Comment: 6 pages, 4 figure
Unusual dynamic charge-density-wave correlations in HgBaCuO
The charge-density-wave (CDW) instability in the underdoped, pseudogap part
of the cuprate phase diagram has been a major recent research focus, yet
measurements of dynamic, energy-resolved CDW correlations are still in their
infancy. We report a high-resolution resonant inelastic X-ray scattering (RIXS)
study of the underdoped cuprate superconductor HgBaCuO ( K). At K, above the CDW order temperature K, we observe significant dynamic CDW correlations at about 40 meV. This
energy scale is comparable to both the superconducting gap and the previously
reported low-energy pseudogap. At , a strong elastic CDW peak appears,
but the dynamic correlations around 40 meV remain virtually unchanged. In
addition, we observe a new feature: dynamic correlations at significantly
higher energy, with a characteristic scale of about 160 meV. A similar scale
was previously identified in other experiments as a high-energy pseudogap. The
existence of three distinct features in the charge response is highly unusual
for a CDW system, and suggests that charge order in the cuprates is closely
related to the pseudogap phenomenon and more complex than previously thought.
We further observe the paramagnon dispersion along [1,0], across the
two-dimensional CDW wavevector , which is
consistent with magnetic excitations measured by inelastic neutron scattering.
Unlike for some other cuprates, our results point to the absence of a
discernible coupling between CDW and magnetic excitations
Charge density waves and Fermi surface reconstruction in the clean overdoped cuprate superconductor Tl2Ba2CuO6+δ
Hall effect and quantum oscillation measurements on high temperature cuprate superconductors show that underdoped compositions have small Fermi surface pockets whereas when heavily overdoped, a single much larger pocket is found. The origin of this change in electronic structure has been unclear, but may be related to the high temperature superconductivity. Here we show that the clean overdoped single-layer cuprate Tl(2)Ba(2)CuO(6+δ) (Tl2201) displays CDW order with a remarkably long correlation length ξ ≈ 200 Å which disappears above a hole doping of p(CDW) ≈ 0.265. We show that the evolution of the electronic properties of Tl2201 as the doping is lowered may be explained by a Fermi surface reconstruction which accompanies the emergence of the CDW below p(CDW). Our results demonstrate importance of CDW correlations in understanding the electronic properties of overdoped cuprates
Magnetic excitations in stripe-ordered LaBaCuO studied using resonant inelastic x-ray scattering
The charge and spin correlations in LaBaCuO (LBCO
1/8) are studied using Cu edge resonant inelastic x-ray scattering
(RIXS). The static charge order (CO) is observed at a wavevector of
and its charge nature confirmed by measuring the dependence of this peak on the
incident x-ray polarization. The paramagnon excitation in LBCO 1/8 is then
measured as it disperses through the CO wavevector. Within the experimental
uncertainty no changes are observed in the paramagnon due to the static CO, and
the paramagnon seems to be similar to that measured in other cuprates, which
have no static CO. Given that the stripe correlation modulates both the charge
and spin degrees of freedom, it is likely that subtle changes do occur in the
paramagnon due to CO. Consequently, we propose that future RIXS measurements,
realized with higher energy resolution and sensitivity, should be performed to
test for these effects.Comment: 5 pages, 4 figure
Collective nature of spin excitations in superconducting cuprates probed by resonant inelastic x-ray scattering
We used resonant inelastic x-ray scattering (RIXS) with and without analysis
of the scattered photon polarization, to study dispersive spin excitations in
the high temperature superconductor YBa2Cu3O6+x over a wide range of doping
levels (0.1 < x < 1). The excitation profiles were carefully monitored as the
incident photon energy was detuned from the resonant condition, and the spin
excitation energy was found to be independent of detuning for all x. These
findings demonstrate that the largest fraction of the spin-flip RIXS profiles
in doped cuprates arises from magnetic collective modes, rather than from
incoherent particle-hole excitations as recently suggested theoretically
[Benjamin et al. Phys. Rev. Lett. 112, 247002(2014)]. Implications for the
theoretical description of the electron system in the cuprates are discussed.Comment: Supplementary materials are available upon reques
Polarization resolved Cu -edge resonant inelastic x-ray scattering of orbital and spin excitations in NdBaCuO
High resolution resonant inelastic x-ray scattering (RIXS) has proven
particularly effective in the determination of crystal field and spin
excitations in cuprates. Its strength lies in the large Cu resonance
and in the fact that the scattering cross section follows quite closely the
single-ion model predictions, both in the insulating parent compounds and in
the superconducting doped materials. However, the spectra become increasingly
broader with (hole) doping, hence resolving and assigning spectral features has
proven challenging even with the highest energy resolution experimentally
achievable. Here we have overcome this limitation by measuring the complete
polarization dependence of the RIXS spectra as function of momentum transfer
and doping in thin films of NdBaCuO. Besides
confirming the previous assignment of and spin excitations (magnon,
bimagnon) in the antiferromagnetic insulating parent compound, we unequivocally
single out the actual spin-flip contribution at all dopings. We also
demonstrate that the softening of excitations is mainly attributed to the
shift of the peak to lower energy loss. These results provide a definitive
assessment of the RIXS spectra of cuprates and demonstrate that RIXS
measurements with full polarization control are practically feasible and highly
informative.Comment: 14 pages, 10 figure
Resonant X-Ray Scattering from CeB
We calculate the resonant x-ray scattering (RXS) spectra near the Ce absorption edge in CeB, on the basis of a microscopic model that the
states of Ce are atomic while the states form an energy band with a
reasonable density of states. In the initial state, we employ an effective
Hamiltonian of Shiina {\it et al}. in the antiferro-quadrupole (AFQ) ordering
phase, while we construct the wave function consistent with the neutron
scattering experiment in the magnetic ground state. In the intermediate state,
we take full account of the intra-atomic Coulomb interaction. Without assuming
any lattice distortion, we obtain sufficient RXS intensities on the AFQ
superlattice spot. We obtain the spectral shape, the temperature and magnetic
field dependences in good agreement with the experiment, thus demonstrating the
mechanism that the intensity is brought about by the modulation of states
through the anisotropic term of the - Coulomb interaction. In the
magnetic ground state, a small pre-edge peak is found by the process. On
the magnetic superlattice spot, we get a finite but considerably small
intensity. The magnetic form factor is briefly discussed.Comment: Latex, 10 pages, 12 figures. To be published in J. Phys. Soc. Jpn.,
Vol.71, No. 7 (2002
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