186 research outputs found
Momentum-dependent charge correlations in YBaCuO superconductors probed by resonant x-ray scattering: Evidence for three competing phases
We have used resonant x-ray scattering to determine the momentum dependent
charge correlations in YBaCuO samples with highly ordered
chain arrays of oxygen acceptors (ortho-II structure). The results reveal
nearly critical, biaxial charge density wave (CDW) correlations at in-plane
wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity
exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length
are enhanced as superconductivity is weakened by an external magnetic field.
Analogous experiments were carried out on a YBaCuO crystal with
a dilute concentration of spinless (Zn) impurities, which had earlier been
shown to nucleate incommensurate magnetic order. Compared to pristine crystals
with the same doping level, the CDW amplitude and correlation length were found
to be strongly reduced. These results indicate a three-phase competition
between spin-modulated, charge-modulated, and superconducting states in
underdoped YBaCuO.Comment: 6 pages, 3 figures revised version, to appear in Phys. Rev. Let
High-energy spin and charge excitations in electron-doped copper oxide superconductors
The evolution of electronic (spin and charge) excitations upon carrier doping
is an extremely important issue in superconducting layered cuprates and the
knowledge of its asymmetry between electron- and hole-dopings is still
fragmentary. Here we combine x-ray and neutron inelastic scattering
measurements to track the doping dependence of both spin and charge excitations
in electron-doped materials. Copper L3 resonant inelastic x-ray scattering
spectra show that magnetic excitations shift to higher energy upon doping.
Their dispersion becomes steeper near the magnetic zone center and deeply mix
with charge excitations, indicating that electrons acquire a highly itinerant
character in the doped metallic state. Moreover, above the magnetic
excitations, an additional dispersing feature is observed near the
{\Gamma}-point, and we ascribe it to particle-hole charge excitations. These
properties are in stark contrast with the more localized spin-excitations
(paramagnons) recently observed in hole-doped compounds even at high
doping-levels.Comment: 20 page
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
Dispersion, damping, and intensity of spin excitations in the single-layer (Bi,Pb)(Sr,La)CuO cuprate superconductor family
Using Cu- edge resonant inelastic x-ray scattering (RIXS) we measured
the dispersion and damping of spin excitations (magnons and paramagnons) in the
high- superconductor (Bi,Pb)(Sr,La)CuO
(Bi2201), for a large doping range across the phase diagram (). Selected measurements with full polarization analysis
unambiguously demonstrate the spin-flip character of these excitations, even in
the overdoped sample. We find that the undamped frequencies increase slightly
with doping for all accessible momenta, while the damping grows rapidly, faster
in the (0,0)(0.5,0.5) nodal direction than in the
(0,0)(0.5,0) antinodal direction. We compare the experimental
results to numerically exact determinant quantum Monte Carlo (DQMC)
calculations that provide the spin dynamical structure factor
of the three-band Hubbard model. The theory reproduces
well the momentum and doping dependence of the dispersions and spectral weights
of magnetic excitations. These results provide compelling evidence that
paramagnons, although increasingly damped, persist across the superconducting
dome of the cuprate phase diagram; this implies that long range
antiferromagnetic correlations are quickly washed away, while short range
magnetic interactions are little affected by doping.Comment: 11 pages, 9 figure
Magnetic excitations and phonons simultaneously studied by resonant inelastic x-ray scattering in optimally doped BiPbSrLaCuO
Magnetic excitations in the optimally doped high-
superconductor BiPbSrLaCuO
(OP-Bi2201, K) are investigated by Cu edge
resonant inelastic x-ray scattering (RIXS), below and above the pseudogap
opening temperature. At both temperatures the broad spectral distribution
disperses along the (1,0) direction up to 350~meV at zone boundary,
similarly to other hole-doped cuprates. However, above 0.22 reciprocal
lattice units, we observe a concurrent intensity decrease for magnetic
excitations and quasi-elastic signals with weak temperature dependence. This
anomaly seems to indicate a coupling between magnetic, lattice and charge modes
in this compound. We also compare the magnetic excitation spectra near the
anti-nodal zone boundary in the single layer OP-Bi2201 and in the bi-layer
optimally doped BiPbSrCaCuO
(OP-Bi2212, K). The strong similarities in the
paramagnon dispersion and in their energy at zone boundary indicate that the
strength of the super-exchange interaction and the short-range magnetic
correlation cannot be directly related to , not even within the
same family of cuprates
Connection between charge-density-wave order and charge transport in the cuprate superconductors
Charge-density-wave (CDW) correlations within the quintessential CuO
planes have been argued to either cause [1] or compete with [2] the
superconductivity in the cuprates, and they might furthermore drive the
Fermi-surface reconstruction in high magnetic fields implied by quantum
oscillation (QO) experiments for YBaCuO (YBCO) [3] and
HgBaCuO (Hg1201) [4]. Consequently, the observation of bulk
CDW order in YBCO was a significant development [5,6,7]. Hg1201 features
particularly high structural symmetry and recently has been demonstrated to
exhibit Fermi-liquid charge transport in the relevant temperature-doping range
of the phase diagram, whereas for YBCO and other cuprates this underlying
property of the CuO planes is partially or fully masked [8-10]. It
therefore is imperative to establish if the pristine transport behavior of
Hg1201 is compatible with CDW order. Here we investigate Hg1201 ( = 72 K)
via bulk Cu L-edge resonant X-ray scattering. We indeed observe CDW
correlations in the absence of a magnetic field, although the correlations and
competition with superconductivity are weaker than in YBCO. Interestingly, at
the measured hole-doping level, both the short-range CDW and Fermi-liquid
transport appear below the same temperature of about 200 K. Our result points
to a unifying picture in which the CDW formation is preceded at the higher
pseudogap temperature by = 0 magnetic order [11,12] and the build-up of
significant dynamic antiferromagnetic correlations [13]. Furthermore, the
smaller CDW modulation wave vector observed for Hg1201 is consistent with the
larger electron pocket implied by both QO [4] and Hall-effect [14]
measurements, which suggests that CDW correlations are indeed responsible for
the low-temperature QO phenomenon
Long-range incommensurate charge fluctuations in (Y,Nd)Ba2Cu3O(6+x)
There are increasing indications that superconductivity competes with other
orders in cuprate superconductors, but obtaining direct evidence with
bulk-sensitive probes is challenging. We have used resonant soft x-ray
scattering to identify two-dimensional charge fluctuations with an
incommensurate periodicity of lattice units in the copper-oxide
planes of the superconductors (Y,Nd)BaCuO with hole
concentrations per planar Cu ion. The intensity and
correlation length of the fluctuation signal increase strongly upon cooling
down to the superconducting transition temperature, ; further cooling
below abruptly reverses the divergence of the charge correlations. In
combination with prior observations of a large gap in the spin excitation
spectrum, these data indicate an incipient charge-density-wave instability that
competes with superconductivity.Comment: to appear in Scienc
Normal-state charge transport in YBa2Cu3O6.67 under uniaxial stress
o provide a foundation for theoretical models of high-temperature superconductivity, experimental research has sought to establish correspondences between macroscopic transport coefficients on the one hand, and atomic-scale correlation functions measured by spectroscopic and scattering probes on the other hand. This research avenue has been confounded by the gradual onset of electronic ordering phenomena and of the corresponding transport anomalies. We report measurements of the uniaxial-stress dependence of the normal-state resistivity and Hall coefficient of the underdoped high-temperature superconductor YBa2Cu3O6.67. We observe a remarkable correspondence between the differential stress responses of the transport coefficients and resonant X-ray diffraction features indicative of charge ordering, which parallels the phenomenology of classical charge-density-wave compounds. However, our observations imply that static charge order is not responsible for a sign reversal of the Hall coefficient, and suggest that the interplay with liquid-like, dynamical charge correlations is essential for the prominent transport anomalies in the underdoped cuprates
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