112 research outputs found
Three dimensional collective charge excitations in electron-doped cuprate superconductors
High temperature cuprate superconductors consist of stacked CuO2 planes, with
primarily two dimensional electronic band structures and magnetic excitations,
while superconducting coherence is three dimensional. This dichotomy highlights
the importance of out-of-plane charge dynamics, believed to be incoherent in
the normal state, yet lacking a comprehensive characterization in
energy-momentum space. Here, we use resonant inelastic x-ray scattering (RIXS)
with polarization analysis to uncover the pure charge character of a recently
discovered collective mode in electron-doped cuprates. This mode disperses
along both the in- and, importantly, out-of-plane directions, revealing its
three dimensional nature. The periodicity of the out-of-plane dispersion
corresponds to the CuO2 plane distance rather than the crystallographic c-axis
lattice constant, suggesting that the interplane Coulomb interaction drives the
coherent out-of-plane charge dynamics. The observed properties are hallmarks of
the long-sought acoustic plasmon, predicted for layered systems and argued to
play a substantial role in mediating high temperature superconductivity.Comment: This is the version of first submission. The revised manuscript
according to peer reviews is now accepted by Nature and will be published
online on 31st Oct., 201
Magnetic correlations in infinite-layer nickelates: an experimental and theoretical multi-method study
We report a comprehensive study of magnetic correlations in LaNiO, a
parent compound of the recently discovered family of infinite-layer (IL)
nickelate superconductors, using multiple experimental and theoretical methods.
Our specific heat, muon-spin rotation (SR), and magnetic susceptibility
measurements on polycrystalline LaNiO show that long-range magnetic order
remains absent down to 2 K. Nevertheless, we detect residual entropy in the
low-temperature specific heat, which is compatible with a model fit that
includes paramagnon excitations. The SR and low-field static and dynamic
magnetic susceptibility measurements indicate the presence of short-range
magnetic correlations and glassy spin dynamics, which we attribute to local
oxygen non-stoichiometry in the average infinite-layer crystal structure. This
glassy behavior can be suppressed in strong external fields, allowing us to
extract the intrinsic paramagnetic susceptibility. Remarkably, we find that the
intrinsic susceptibility shows non-Curie-Weiss behavior at high temperatures,
in analogy to doped cuprates that possess robust non-local spin fluctuations.
The distinct temperature dependence of the intrinsic susceptibility of
LaNiO can be theoretically understood by a multi-method study of the
single-band Hubbard model in which we apply complementary cutting-edge quantum
many-body techniques (dynamical mean-field theory, cellular dynamical
mean-field theory and the dynamical vertex approximation) to investigate the
influence of both short- and long-ranged correlations. Our results suggest a
profound analogy between the magnetic correlations in parent (undoped) IL
nickelates and doped cuprates.Comment: 18 pages, 14 figure
Synchrotron x ray scattering study of charge density wave order in HgBa2CuO4 delta
We present a detailed synchrotron x-ray scattering study of the
charge-density-wave (CDW) order in simple tetragonal HgBaCuO
(Hg1201). Resonant soft x-ray scattering measurements reveal that short-range
order appears at a temperature that is distinctly lower than the pseudogap
temperature and in excellent agreement with a prior transient reflectivity
result. Despite considerable structural differences between Hg1201 and
YBaCuO, the CDW correlations exhibit similar doping
dependencies, and we demonstrate a universal relationship between the CDW wave
vector and the size of the reconstructed Fermi pocket observed in quantum
oscillation experiments. The CDW correlations in Hg1201 vanish already below
optimal doping, once the correlation length is comparable to the CDW modulation
period, and they appear to be limited by the disorder potential from unit cells
hosting two interstitial oxygen atoms. A complementary hard x-ray diffraction
measurement, performed on an underdoped Hg1201 sample in magnetic fields along
the crystallographic axis of up to 16 T, provides information about the
form factor of the CDW order. As expected from the single-CuO-layer
structure of Hg1201, the CDW correlations vanish at half-integer values of
and appear to be peaked at integer . We conclude that the atomic
displacements associated with the short-range CDW order are mainly planar,
within the CuO layers
Evolution of plasmon excitations across the phase diagram of the cuprate superconductor LaSrCuO
We use resonant inelastic x-ray scattering (RIXS) at the O - and Cu
-edges to investigate the doping- and temperature dependence of low-energy
plasmon excitations in LaSrCuO. We observe a monotonic
increase of the energy scale of the plasmons with increasing doping in the
underdoped regime, whereas a saturation occurs above optimal doping and persists at least up to . Furthermore, we find that the
plasmon excitations show only a marginal temperature dependence, and possible
effects due to the superconducting transition and the onset of strange metal
behavior are either absent or below the detection limit of our experiment.
Taking into account the strongly correlated character of the cuprates, we show
that layered -- model calculations accurately capture the increase of
the plasmon energy in the underdoped regime. However, the computed plasmon
energy continues to increase even for doping levels above ,
which is distinct from the experimentally observed saturation, and reaches a
broad maximum around . We discuss whether possible lattice disorder
in overdoped samples, a renormalization of the electronic correlation strength
at high dopings, or an increasing relevance of non-planar Cu and O orbitals
could be responsible for the discrepancy between experiment and theory for
doping levels above .Comment: 19 pages, 11 figure
Genetic distinctiveness of rye in situ accessions from Portugal unveils a new hotspot of unexplored genetic resources
Rye(SecalecerealeL.)is a cereal crop of major importance in many parts of Europe and rye breeders are presently very concerned with th e restrict pool of rye genetic resources available.Such narrowing of rye genetic diversity results from the presence of“Petkus ”pool in most modern rye varieties as well as “Petkus”דCarsten” heterotic pool in hybrid rye breeding programs.Previous studies on rye’s genetic diversity revealed more over a common genetic background on landraces(exsitu) and cultivars,regardless of breeding level or geographical origin.Thus evaluation of in situ populations is of utmost importance to unveil “onfarm” diversity,which is largely undervalued.Here,we perform the first comprehensive assess ment of rye’s genetic diversity and population structuring using cultivars,exsitu landraces along a comprehensive sampling of insitu accessions from Portugal,through amolecular-directed analysis using SSRs markers.Rye genetic diversity and population structure analysis does not present any geographical trend but disclosed marked differences between genetic backgrounds of in situ accessions and those of cultivars/exsitu collections.Such genetic distinctiveness of insitu accessions highlights their unexplored potential as new genetic resources,which can be used to boost rye breeding strategies and the production of new varieties.Overall,our study successfully demonstrates the high prospective impact of comparing genetic diversity and structure of cultivars,exsitu,and in situ samples in ascertaining the status of plant genetic resources (PGR)info:eu-repo/semantics/publishedVersio
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