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We conducted a comparative study of the rare-earth infinite-layer nickelates films, RNiO2 (R = La, Pr, and Nd) using resonant inelastic X-ray scattering (RIXS). We found that the gross features of the orbital configurations are essentially the same, with minor variations in the detailed hybridization. For low-energy excitations, we unambiguously confirm the presence of damped magnetic excitations in all three compounds. By fitting to a linear spin-wave theory, comparable spin exchange coupling strengths and damping coefficients are extracted, indicating a universal magnetic structure in the infinite-layer nickelates. Interestingly, while signatures of a charge order are observed in LaNiO2 in the quasi-elastic region of the RIXS spectrum, it is absent in NdNiO2 and PrNiO2. This prompts further investigation into the universality and the origins of charge order within the infinite-layer inickelates., Comment: 8 figures. Accepted by Physical Review B

Analyzing the effects of space weather on aviation is a new and developing topic. It has been commonly accepted that the flight time of the polar flights may increase during solar proton events because the flights have to change their route to avoid the high-energy particles. However, apart from such phenomenon, researches related to the flight time during space weather events is very rare. Based on the analyses of 39 representative international air routes around westerlies, it is found that 97.44% (94.87%) of the commercial airplanes on the westbound (eastbound) air routes reveal shorter (longer) flight time during solar proton events compared to those during quiet periods, and the averaged magnitude of change in flight time is ~10 min or 0.21%-4.17% of the total flight durations. Comparative investigations reassure the certainty of such phenomenon that the directional differences in flight time are still incontrovertible regardless of over-land routes (China-Europe) or over-sea routes (China-Western America). Further analyses suggest that the solar proton events associated atmospheric heating will change the flight durations by weakening certain atmospheric circulations, such as the polar jet stream. While the polar jet stream will not be obviously altered during solar flares so that the directional differences in flight time are not found. Besides the conventional space weather effects already known, this paper is the first report that indicates a distinct new scenario of how the solar proton events affect flight time. These analyses are also important for aviation since our discoveries could help the airways optimize the air routes to save passenger time costs, reduce fuel costs and even contribute to the global warming issues., Comment: submitted to Scientific Reports

Solar flare is one of the severest solar activities on the sun, and it has many important impacts on the near-earth space. It has been found that flight arrival delays will increase during solar flare. However, the detailed intrinsic mechanism of how solar flares influence the delays is still unknown. Based on 5-years huge amount of flight data, here we comprehensively analyze the flight departure delays during 57 solar flares. It is found that the averaged flight departure delay time during solar flares increased by 20.68% (7.67 min) compared to those during quiet periods. It is also shown that solar flare related flight delays reveal apparent time and latitude dependencies. Flight delays during dayside solar flares are more serious than those during nightside flares, and the longer (shorter) delays tend to occur in the lower (higher) latitude airport. Further analyses suggest that flight delay time and delay rate would be directly modulated by the solar intensity (soft X-ray flux) and the Solar Zenith Angle. For the first time, these results indicate that the communication interferences caused by solar flares will directly affect flight departure delay time and delay rate. This work also expands our conventional understandings to the impacts of solar flares on human society, and it could also provide us with brand new views to help prevent or cope with flight delays., Comment: submitted to APJL

Although the sun is really far away from us, some solar activities could still influence the performance and reliability of space-borne and ground-based technological systems on Earth. Those time-varying conditions in space caused by the sun are also called space weather, as the atmospheric conditions that can affect weather on the ground. It is known that aviation activities can be affected during space weather events, but the exact effects of space weather on aviation are still unclear. Especially how the flight delays, the top topic concerned by most people, will be affected by space weather has never been thoroughly researched. By analyzing huge amount of flight data (~5X106 records), for the first time, we demonstrate that space weather events could have systematically modulating effects on flight delays. The average arrival delay time and 30-minute delay rate during space weather events are significantly increased by 81.34% and 21.45% respectively compared to those during quiet periods. The evident negative correlation between the yearly flight regularity rate and the yearly mean total sunspot number during 22 years also confirms such delay effects. Further studies indicate that the interference in communication and navigation caused by geomagnetic field fluctuations and ionospheric disturbances associated with the space weather events will increase the flight delay time and delay rate. These results expand the traditional field of space weather research and could also provide us with brand new views for improving the flight delay predications., Comment: submitted to science advances

The discovery of superconductivity in infinite-layer nickelates brings us tantalizingly close to a new material class that mirrors the cuprate superconductors. Here, we report on magnetic excitations in these nickelates, measured using resonant inelastic x-ray scattering (RIXS) at the Ni L3-edge, to shed light on the material complexity and microscopic physics. Undoped NdNiO2 possesses a branch of dispersive excitations with a bandwidth of approximately 200 meV, reminiscent of strongly-coupled, antiferromagnetically aligned spins on a square lattice, despite a lack of evidence for long range magnetic order. The significant damping of these modes indicates the importance of coupling to rare-earth itinerant electrons. Upon doping, the spectral weight and energy decrease slightly, while the modes become overdamped. Our results highlight the role of Mottness in infinite-layer nickelates., Comment: This is the initially submitted version before revising for reviewers' comments. The peer-reviewed version has been accepted at Science and will be published soon

The recent discovery of superconductivity in Nd$_{1-x}$Sr$_{x}$NiO$_2$ has drawn significant attention in the field. A key open question regards the evolution of the electronic structure with respect to hole doping. Here, we exploit x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the doping dependent electronic structure of the NiO$_2$ planes. Upon doping, a higher energy feature in Ni $L_3$ edge XAS develops in addition to the main absorption peak. By comparing our data to atomic multiplet calculations including $D_{4h}$ crystal field, the doping induced feature is consistent with a $d^8$ spin singlet state, in which doped holes reside in the $d_{x^2-y^2}$ orbitals, similar to doped single band Hubbard models. This is further supported by orbital excitations observed in RIXS spectra, which soften upon doping, corroborating with Fermi level shift associated with increasing holes in the $d_{x^2-y^2}$ orbital., Comment: 6 pages, 4 figures. Supplemental material included

We have completed a measurement of the $(6s^26p^2)\, ^3\!P_0 \rightarrow \, ^3\!P_2$ 939 nm electric quadrupole ($E2$) transition amplitude in atomic lead. Using a Faraday rotation spectroscopy technique and a sensitive polarimeter, we have measured this very weak $E2$ transition for the first time, and determined its amplitude to be $\langle ^3\!P_2 || Q || ^3\!P_0 \rangle$ = 8.91(9) a.u.. We also present an ab initio theoretical calculation of this matrix element, which agrees with experiment at the 0.5\% level. We heat a quartz vapor cell containing $^{208}$Pb to between 800 and 940 $^{\circ}$C, apply a $\sim \! 10 \, {\rm G}$ longitudinal magnetic field, and use polarization modulation/lock-in detection to measure optical rotation amplitudes of order 1 mrad with noise near 1 $\mu$rad. We compare the Faraday rotation amplitude of the $E2$ transition to that of the $^3\!P_0 -\, ^3\!P_1$ 1279 nm magnetic dipole ($M1$) transition under identical sample conditions.

We report measurements of the $^{115}$In $7p_{1/2}$ and $7p_{3/2}$ scalar and tensor polarizabilities using two-step diode laser spectroscopy in an atomic beam. The scalar polarizabilities are one to two orders of magnitude larger than for lower lying indium states due to the close proximity of the $7p$ and $6d$ states. For the scalar polarizabilities, we find values (in atomic units) of $1.811(4) \times 10^5$ $a_0^3$ and $2.876(6) \times 10^5$ $a_0^3$ for the $7p_{1/2}$ and $7p_{3/2}$ states respectively. We estimate the smaller tensor polarizability component of the $7p_{3/2}$ state to be $-1.43(18) \times 10^4$ $a_0^3$. These measurements represent the first high-precision benchmarks of transition properties of such high excited states of trivalent atomic systems. We also present new ab initio calculations of these quantities and other In polarizabilities using two high-precision relativistic methods to make a global comparison of the accuracies of the two approaches. The precision of the experiment is sufficient to differentiate between the two theoretical methods as well as to allow precise determination of the indium $7p-6d$ matrix elements. The results obtained in this work are applicable to other heavier and more complicated systems, and provide much needed guidance for the development of even more precise theoretical approaches., Comment: 12 pages, 8 figures corrected two typos in version 2

A two-step, two-color laser spectroscopy technique has been used to measure the hyperfine splittings of the $8p$ excited states in $^{203}$Tl and $^{205}$Tl, as well as the $7s - 8p$ transition isotope shifts. For the case of the $8p_{3/2}$ state, our results show a hyperfine anomaly consistent with our recent measurements of other hyperfine splittings, and in disagreement with older results for this state. Our measurement of the $8p_{1/2}$ isotope shift is also in disagreement with earlier work. In this series of experiments, a UV laser was locked to the first-step transition and directed through a heated vapor cell, while a second spatially overlapping red laser was scanned across the two second-step transitions. To facilitate accurate frequency calibration, radio-frequency modulation of the second-step laser was used to create sidebands in the Doppler-free absorption spectrum., Comment: arXiv admin note: text overlap with arXiv:1310.7216

This study investigates the strong photoluminescence (PL) and X-ray excited optical luminescence observed in nitrogen-functionalized 2D graphene nanoflakes (GNFs:N), which arise from the significantly enhanced density of states in the region of {\pi} states and the gap between {\pi} and {\pi}* states. The increase in the number of the sp2 clusters in the form of pyridine-like N-C, graphite-N-like, and the C=O bonding and the resonant energy transfer from the N and O atoms to the sp2 clusters were found to be responsible for the blue shift and the enhancement of the main PL emission feature. The enhanced PL is strongly related to the induced changes of the electronic structures and bonding properties, which were revealed by the X-ray absorption near-edge structure, X-ray emission spectroscopy, and resonance inelastic X-ray scattering. The study demonstrates that PL emission can be tailored through appropriate tuning of the nitrogen and oxygen contents in GNFs and pave the way for new optoelectronic devices., Comment: 8 pages, 6 figures (including toc figure)