The quasi-2D nickelate La4Ni3O8 (La-438), consisting of trilayer networks of square planar Ni ions, is a member of the so-called T' family, which is derived from the Ruddlesden-Popper (R-P) parent ...compound La4Ni3O10-x by removing two oxygen atoms and rearranging the rock salt layers to fluorite-type layers. Although previous studies on polycrystalline samples have identified a 105-K phase transition with a pronounced electronic and magnetic response but weak lattice character, no consensus on the origin of this transition has been reached. Here, we show using synchrotron X-ray diffraction on high-pO2 floating zone-grown single crystals that this transition is associated with a real space ordering of charge into a quasi-2D charge stripe ground state. The charge stripe superlattice propagation vector, q = (2/3, 0, 1), corresponds with that found in the related 1/3-hole doped single-layer R-P nickelate, La5/3Sr1/3NiO4 (LSNO-1/3; Ni(2.33+)), with orientation at 45° to the Ni-O bonds. The charge stripes in La-438 are weakly correlated along c to form a staggered ABAB stacking that reduces the Coulomb repulsion among the stripes. Surprisingly, however, we find that the charge stripes within each trilayer of La-438 are stacked in phase from one layer to the next, at odds with any simple Coulomb repulsion argument.
Feedback analysis in climate models commonly involves decomposing any change in the system’s energy balance into radiative forcing terms due to prescribed changes, and response terms due to the ...radiative effects of changes in model variables such as temperature, water vapor, clouds, sea ice, and snow. The established “partial radiative perturbation” (PRP) method allows an accurate separation of these terms, but requires processing large volumes of model output with an offline version of the model’s radiation code. Here, we propose an “approximate PRP” (APRP) method for the shortwave that provides an accurate estimate of the radiative perturbation, but derived from a quite modest amount of monthly mean model output.
The APRP method is based on a simplified shortwave radiative model of the atmosphere, where surface absorption and atmospheric scattering and absorption are represented by means of three parameters that are diagnosed for overcast and clear-sky portions of each model grid cell. The accuracy of the method is gauged relative to full PRP calculations in two experiments: one in which carbon dioxide concentration is doubled and another in which conditions of the Last Glacial Maximum (LGM) are simulated. The approximate PRP method yields a shortwave cloud feedback accurate in the global mean to within 7%. Forcings and feedbacks due to surface albedo and noncloud atmospheric constituents are also well approximated with errors of order 5%–10%. Comparison of two different model simulations of the LGM shows that the regional and global differences in their ice sheet albedo forcing fields are clearly captured by the APRP method. Hence this method is an efficient and satisfactory tool for studying and intercomparing shortwave forcing and feedbacks in climate models.
In acute myeloid leukaemia, long-term survival is poor as most patients relapse despite achieving remission. Historically, the failure of therapy has been thought to be due to mutations that produce ...drug resistance, possibly arising as a consequence of the mutagenic properties of chemotherapy drugs. However, other lines of evidence have pointed to the pre-existence of drug-resistant cells. For example, deep sequencing of paired diagnosis and relapse acute myeloid leukaemia samples has provided direct evidence that relapse in some cases is generated from minor genetic subclones present at diagnosis that survive chemotherapy, suggesting that resistant cells are generated by evolutionary processes before treatment and are selected by therapy. Nevertheless, the mechanisms of therapy failure and capacity for leukaemic regeneration remain obscure, as sequence analysis alone does not provide insight into the cell types that are fated to drive relapse. Although leukaemia stem cells have been linked to relapse owing to their dormancy and self-renewal properties, and leukaemia stem cell gene expression signatures are highly predictive of therapy failure, experimental studies have been primarily correlative and a role for leukaemia stem cells in acute myeloid leukaemia relapse has not been directly proved. Here, through combined genetic and functional analysis of purified subpopulations and xenografts from paired diagnosis/relapse samples, we identify therapy-resistant cells already present at diagnosis and two major patterns of relapse. In some cases, relapse originated from rare leukaemia stem cells with a haematopoietic stem/progenitor cell phenotype, while in other instances relapse developed from larger subclones of immunophenotypically committed leukaemia cells that retained strong stemness transcriptional signatures. The identification of distinct patterns of relapse should lead to improved methods for disease management and monitoring in acute myeloid leukaemia. Moreover, the shared functional and transcriptional stemness properties that underlie both cellular origins of relapse emphasize the importance of developing new therapeutic approaches that target stemness to prevent relapse.
In this study we examine the anthropogenically forced climate response over the historical period, 1860 to present, and projected response to 2100, using updated emissions scenarios and an improved ...coupled model (HadCM3) that does not use flux adjustments. We concentrate on four new Special Report on Emission Scenarios (SRES) namely (A1FI, A2, B2, B1) prepared for the Intergovernmental Panel on Climate Change Third Assessment Report, considered more self-consistent in their socio-economic and emissions structure, and therefore more policy relevant, than older scenarios like IS92a. We include an interactive model representation of the anthropogenic sulfur cycle and both direct and indirect forcings from sulfate aerosols, but omit the second indirect forcing effect through cloud lifetimes. The modelled first indirect forcing effect through cloud droplet size is near the centre of the IPCC uncertainty range. We also model variations in tropospheric and stratospheric ozone. Greenhouse gas-forced climate change response in B2 resembles patterns in IS92a but is smaller. Sulfate aerosol and ozone forcing substantially modulates the response, cooling the land, particularly northern mid-latitudes, and altering the monsoon structure. By 2100, global mean warming in SRES scenarios ranges from 2.6 to 5.3 K above 1900 and precipitation rises by 1%/K through the twenty first century (1.4%/K omitting aerosol changes). Large-scale patterns of response broadly resemble those in an earlier model (HadCM2), but with important regional differences, particularly in the tropics. Some divergence in future response occurs across scenarios for the regions considered, but marked drying in the mid-USA and southern Europe and significantly wetter conditions for South Asia, in June-July-August, are robust and significant.PUBLICATION ABSTRACT
The discovery of superconductivity in a d9−δ nickelate has inspired disparate theoretical perspectives regarding the essential physics of this class of materials. A key issue is the magnitude of the ...magnetic superexchange, which relates to whether cuprate-like high-temperature nickelate superconductivity could be realized. We address this question using Ni L-edge and O K-edge spectroscopy of the reduced d9−1/3 trilayer nickelates R4Ni3O8 (where R = La Pr) and associated theoretical modeling. A magnon energy scale of ∼ 80 meV resulting from a nearest-neighbor magnetic exchange of J = 69 (4) meV is observed, proving that d9−δ nickelates can host a large superexchange. This value, along with that of the Ni-O hybridization estimated from our O K -edge data, implies that trilayer nickelates represent an intermediate case between the infinite-layer nickelates and the cuprates. Layered nickelates thus provide a route to testing the relevance of superexchange to nickelate superconductivity.
An extreme magnetoresistance (XMR) has recently been observed in several nonmagnetic semimetals. Increasing experimental and theoretical evidence indicates that the XMR can be driven by either ...topological protection or electron-hole compensation. Here, by investigating the electronic structure of a XMR material, YSb, we present spectroscopic evidence for a special case which lacks topological protection and perfect electron-hole compensation. Further investigations reveal that a cooperative action of a substantial difference between electron and hole mobility and a moderate carrier compensation might contribute to the XMR in YSb.
Abstract
Nickelates are a rich class of materials, ranging from insulating magnets to superconductors. But for stoichiometric materials, insulating behavior is the norm, as for most late transition ...metal oxides. Notable exceptions are the 3D perovskite LaNiO
3
, an unconventional paramagnetic metal, and the layered Ruddlesden-Popper phases R
4
Ni
3
O
10
, (R = La, Pr, Nd). The latter are particularly intriguing because they exhibit an unusual metal-to-metal transition. Here, we demonstrate that this transition results from an incommensurate density wave with both charge and magnetic character that lies closer in its behavior to the metallic density wave seen in chromium metal than the insulating stripes typically found in single-layer nickelates like La
2-
x
Sr
x
NiO
4
. We identify these intertwined density waves as being Fermi surface-driven, revealing a novel ordering mechanism in this nickelate that reflects a coupling among charge, spin, and lattice degrees of freedom that differs not only from the single-layer materials, but from the 3D perovskites as well.
In this paper, the spin and parity of the Zc(3900)± state are determined to be JP = 1+ with a statistical significance larger than 7σ over other quantum numbers in a partial wave analysis of the ...process e+e- → π+π-J/Ψ. We use a data sample of 1.92 fb-1 accumulated at $ \sqrt{s}=4.23 $ and 4.26 GeV with the BESIII experiment. When parametrizing the Zc(3900)± with a Flatté-like formula, we determine its pole mass Mpole = (3881.2±4.2stat ±52.7syst) MeV/c2 and pole width Γpole = (51.8± 4.6stat ± 36.0syst) MeV. Finally, we also measure cross sections for the process e+e- → Zc(3900)+π- + c.c. → J/Ψπ+π- and determine an upper limit at the 90% confidence level for the process e+e- → Zc(4020)+π- + c.c. → J/Ψ π+π-.
Using a data sample corresponding to an integrated luminosity of 2.93 fb−1 taken at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we perform an ...analysis of the semileptonic decays D0(+)→π−(0)μ+νμ. The branching fractions of D0→π−μ+νμ and D+→π0μ+νμ are measured to be (0.272±0.008stat±0.006syst)% and (0.350±0.011stat±0.010syst)%, respectively, where the former is of much improved precision compared to previous results and the latter is determined for the first time. Using these results along with previous BESIII measurements of D0(+)→π−(0)e+νe, we calculate the branching fraction ratios to be R0≡BD0→π−μ+νμ/BD0→π−e+νe=0.922±0.030stat±0.022syst and R+≡BD+→π0μ+νμ/BD+→π0e+νe=0.964±0.037stat±0.026syst, which are compatible with the theoretical expectation of lepton flavor universality within 1.7σ and 0.5σ, respectively. We also examine the branching fraction ratios in different four-momentum transfer square regions, and find no significant deviations from the standard model predictions.
Charge order is a central feature of the physics of cuprate superconductors and is known to arise from a modulation of holes with primarily oxygen character. Low-valence nickelate superconductors ...also host charge order, but the electronic character of this symmetry breaking is unsettled. Here, using resonant inelastic x-ray scattering at the NiL2edge, we identify intertwined involvements of Ni3dx2−y2,3d3z2−r2, and O2pσorbitals in the formation of diagonal charge order in an overdoped low-valence nickelateLa4Ni3O8. The Ni3dx2−y2orbitals, strongly hybridized with planar O2pσ, largely shape the spatial charge distribution and lead to Ni site-centered charge order. The3d3z2−r2orbitals play a small, but non-negligible role in the charge order as they hybridize with the rare-earth5dorbitals. Our results reveal that the low-energy physics and ground-state character of these nickelates are more complex than those in cuprates.
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