Orbital breathing effects in the computation of x-ray d-ion spectra in solids by ab initio wave-function-based methods

In existing theoretical approaches to core-level excitations of transition-metal ions in solids relaxation and polarization effects due to the inner core hole are often ignored or described phenomenologically. Here we set up an ab initio computational scheme that explicitly accounts for such physics in the calculation of x-ray absorption and resonant inelastic x-ray scattering spectra. Good agreement is found with experimental transition-metal $L$-edge data for the strongly correlated $d^9$ cuprate Li$_2$CuO$_2$, for which we determine the absolute scattering intensities. The newly developed methodology opens the way for the investigation of even more complex $d^n$ electronic structures of group VI B to VIII B correlated oxide compounds

Localized vs. delocalized character of charge carriers in LaAlO3/ SrTiO3 superlattices

Understanding the nature of electrical conductivity, superconductivity and magnetism between layers of oxides is of immense importance for the design of electronic devices employing oxide heterostructures. We demonstrate that resonant inelastic X-ray scattering can be applied to directly probe the carriers in oxide heterostructures. Our investigation on epitaxially grown LaAlO3/SrTiO3 superlattices unambiguously reveals the presence of both localized and delocalized Ti 3d carriers. These two types of carriers are caused by oxygen vacancies and electron transfer due to the polar discontinuity at the interface. This result allows explaining the reported discrepancy between theoretically calculated and experimentally measured carrier density values in LaAlO3/SrTiO3 heterostructures.Comment: 14 pages, 3 figure

Analysis of air quality changes and causes in the Liaoning region from 2017 to 2022

Using the air quality monitoring data from the Department of Ecology and Environment of Liaoning Province for the period from 2017 to 2022, the temporal and spatial changes in the concentrations of various air pollutants in the Liaoning region for the periods from 2017 to 2019 and 2020 to 2022 were analyzed by using the Evaluation on the meteorological condition index of PM2.5 pollution (EMI) and the ArcGIS Kriging Interpolation Method, and the contributions of pollution reduction to the changes in the air quality of the Liaoning region were assessed. The results show that after the implementation of emission reduction measures, the quality of the atmospheric environment in the Liaoning region has significantly improved, and the mean concentrations of PM2.5, PM10, SO2, NO2, CO and O3 are all reduced by a certain magnitude in the period 2020 to 2022 compared with the period 2017 to 2019; Based on the EMI index calculation, the average EMI index in Liaoning during the period 2020 to 2022 is about 1.7% lower than the average value of the region during the period 2017 to 2019, and the atmospheric dispersion conditions are relatively good; From the perspective of daily changes in pollutant concentrations, the trend of PM2.5 and PM10 concentrations changed from double peaks and single valleys to single peaks and single valleys, and there were no significant changes in the types of valleys for CO, SO2, NO2, and O3, whereas the peaks of O3 concentrations during the daytime were basically the same as in previous years, and the concentrations during the nighttime were slightly higher than in previous years. Classification by topographic areas revealed that the mean pollutant concentration for the period from 2017 to 2019 was more significant than the mean value for the period from 2020 to 2022, except for O3, where the air quality in the mountainous areas of Liaodong and Liaoxi was better than that of the Liaohe Plain, and regional classification by coastal and inland, where the air quality in the coastal areas was better than that of the inland areas

Paramagnons and high-temperature superconductivity in a model family of cuprates

Cuprate superconductors have the highest critical temperatures (Tc) at ambient pressure, yet a consensus on the superconducting mechanism remains to be established. Finding an empirical parameter that limits the highest reachable Tc can provide crucial insight into this outstanding problem. Here, in the first two Ruddlesden-Popper members of the model Hg- family of cuprates, which are chemically nearly identical and have the highest Tc among all cuprate families, we use inelastic photon scattering to reveal that the energy of magnetic fluctuations may play such a role. In particular, we observe the single-paramagnon spectra to be nearly identical between the two compounds, apart from an energy scale difference of ~30% which matches their difference in Tc. The empirical correlation between paramagnon energy and maximal Tc is further found to extend to other cuprate families with relatively high Tc’s, hinting at a fundamental connection between them

Orbital selective coupling in CeRh3_3B2_2: co-existence of high Curie and high Kondo temperature

We investigated the electronic structure of the enigmatic CeRh$_3$B$_2$ using resonant inelastic scattering and x-ray absorption spectroscopy in combination with $ab$ $initio$ density functional calculations. We find that the Rh 4$d$ states are irrelevant for the high-temperature ferromagnetism and the Kondo effect. We also find that the Ce 4$f$ crystal-field strength is too small to explain the strong reduction of the Ce magnetic moment. The data reveal instead the presence of two different active Ce 4$f$ orbitals, with each coupling selectively to different bands in CeRh$_3$B$_2$. The inter-site hybridization of the |J=5/2,Jz=+/-1/2> crystal-field state and Ce 5$d$ band combined with the intra-site Ce 4$f$-5$d$ exchange creates the strong ferromagnetism, while hybridization between the |J=5/2,Jz=+/-5/2> and the B $sp$ in the $ab$-plane contributes to the Kondo interaction which causes the moment reduction. This orbital selective coupling explains the unique and seemingly contradictory properties of CeRh$_3$B$_2$.Comment: 15 pages, 14 figure

Precise let-7 expression levels balance organ regeneration against tumor suppression

The in vivo roles for even the most intensely studied microRNAs remain poorly defined. Here, analysis of mouse models revealed that let-7, a large and ancient microRNA family, performs tumor suppressive roles at the expense of regeneration. Too little or too much let-7 resulted in compromised protection against cancer or tissue damage, respectively. Modest let-7 overexpression abrogated MYC-driven liver cancer by antagonizing multiple let-7 sensitive oncogenes. However, the same level of overexpression blocked liver regeneration, while let-7 deletion enhanced it, demonstrating that distinct let-7 levels can mediate desirable phenotypes. let-7 dependent regeneration phenotypes resulted from influences on the insulin-PI3K-mTOR pathway. We found that chronic high-dose let-7 overexpression caused liver damage and degeneration, paradoxically leading to tumorigenesis. These dose-dependent roles for let-7 in tissue repair and tumorigenesis rationalize the tight regulation of this microRNA in development, and have important implications for let-7 based therapeutics. DOI: http://dx.doi.org/10.7554/eLife.09431.00