Abstract
Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, ...was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd
3
to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature—the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.
The topology of electronic and phonon band structures of graphene is well studied and known to exhibit a Dirac cone at the K point of the Brillouin zone. Here, we applied inelastic x-ray scattering ...(IXS) along with ab initio calculations to investigate phonon topology in graphite, the 3D analog of graphene. We identified a pair of modes that form a very weakly gapped linear anticrossing at the K point that can be essentially viewed as a Dirac cone approximant. The IXS intensity in the vicinity of the quasi-Dirac point reveals a harmonic modulation of the phonon spectral weight above and below the Dirac energy, which was previously proposed as an experimental fingerprint of the nontrivial topology. We illustrate how the topological winding of IXS intensity can be understood in terms of atomic displacements and highlight that the intensity winding is not in fact sensitive in telling quasi- and true Dirac points apart.
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Emissions estimates of anthropogenic methane (CH4) sources are highly uncertain and many sources related to energy production are localized yet difficult to quantify. Airborne imaging spectrometers ...like the next generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) are well suited for locating CH4 point sources due to their ability to map concentrations over large regions with the high spatial resolution necessary to resolve localized emissions. AVIRIS-NG was deployed during a field campaign to measure controlled CH4 releases at the Rocky Mountain Oilfield Testing Center (RMOTC) in Wyoming, U.S. for multiple flux rates and flight altitudes. Two algorithms were applied to AVIRIS-NG scenes, a matched filter detection algorithm and a hybrid retrieval approach using the Iterative Maximum a Posteriori Differential Optical Absorption Spectroscopy (IMAP-DOAS) algorithm and Singular Value Decomposition. Plumes for releases as low as 14.16m3/h (0.09kt/year) were consistently observed by AVIRIS-NG at multiple flight altitudes and images of plumes were in agreement with wind directions measured at ground stations. In some cases plumes as low as 3.40m3/h (0.02kt/year) were detected, indicating that AVIRIS-NG has the capability of detecting a wide range of fugitive CH4 source categories for natural gas fields. This controlled release experiment is the first of its kind using AVIRIS-NG and demonstrates the utility of imaging spectrometers for direct attribution of emissions to individual point source locations. This is particularly useful given the large uncertainties associated with anthropogenic CH4 emissions, including those from industry, gas transmission lines, and the oil and gas sectors.
•AVIRIS-NG detected CH4 plumes for fluxes as low as 3.4m3/h (0.02kt/year).•Plumes observed for flights between 0.43 and 3.80km above ground level.•Plume shape and orientation consistent with observed wind speed and direction•AVIRIS-NG capable of detecting emission sources in existing gas fields
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We advertise rare-earth intermetallics with high-symmetry crystal structures and competing interactions as a possible materials platform hosting spin structures with non-trivial topological ...properties. Focusing on the series of cubic
Cu compounds, where
= Ho, Er, Tm, the bulk properties of these systems display exceptionally rich magnetic phase diagrams hosting an abundance of different phase pockets characteristic of antiferromagnetic order in the presence of delicately balanced interactions. The electrical transport properties exhibit large anomalous contributions suggestive of topologically non-trivial winding in the electronic and magnetic structures. Neutron diffraction identifies spontaneous long-range magnetic order in terms of commensurate and incommensurate variations of(ππ0)antiferromagnetism with the possibility for various multi-
configurations. Motivated by general trends in these materials, we discuss the possible existence of topologically non-trivial winding in real and reciprocal space in the class of
Cu compounds including antiferromagnetic skyrmion lattices. Putatively bringing together different limits of non-trivial topological winding in the same material, the combination of properties in
Cu systems promises access to advanced functionalities.
We have performed powder inelastic neutron scattering measurements on the unconventional superconductor beta - FeSe (T sub(c) Asymptotically = to 8 K). The spectra reveal highly dispersive ...paramagnetic fluctuations emerging from the square-lattice wave vector (pi, 0) extending beyond 80 meV in energy. Measurements as a function of temperature at an energy of ~ 13 meV did not show any variation from T sub(c) to 104 K. The results show that FeSe is close to an instability towards (pi, 0) antiferromagnetism that is characteristic of the parent phases of the high-T sub(c) iron arsenide superconductors, and that the iron paramagnetic moment is neither affected by the orthorhombic-to-tetragonal structural transition at T sub(s) Asymptotically = to 90 K nor does it undergo a change in spin state over the temperature range studied.
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DNA replication occurs in microscopically visible complexes at discrete sites (replication foci) in the nucleus. These foci consist of DNA associated with replication machineries, i.e., large protein ...complexes involved in DNA replication. To study the dynamics of these nuclear replication foci in living cells, we fused proliferating cell nuclear antigen (PCNA), a central component of the replication machinery, with the green fluorescent protein (GFP). Imaging of stable cell lines expressing low levels of GFP-PCNA showed that replication foci are heterogeneous in size and lifetime. Time-lapse studies revealed that replication foci clearly differ from nuclear speckles and coiled bodies as they neither show directional movements, nor do they seem to merge or divide. These four dimensional analyses suggested that replication factories are stably anchored in the nucleus and that changes in the pattern occur through gradual, coordinated, but asynchronous, assembly and disassembly throughout S phase.
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We report theoretical and experimental evidence that EuCd2As2 in magnetic fields greater than 1.6 T applied along the c axis is a Weyl semimetal with a single pair of Weyl nodes. Ab initio electronic ...structure calculations, verified at zero field by angle-resolved photoemission spectra, predict Weyl nodes with wave vectors k=(0,0,±0.03)×2π/c at the Fermi level when the Eu spins are fully aligned along the c axis. Shubnikov–de Haas oscillations measured in fields parallel to c reveal a cyclotron effective mass of mc*=0.08me and a Fermi surface of extremal area Aext=0.24nm−2, corresponding to 0.1% of the area of the Brillouin zone. The small values of mc* and Aext are consistent with quasiparticles near a Weyl node. The identification of EuCd2As2 as a model Weyl semimetal opens the door to fundamental tests of Weyl physics.
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Nematic State in CeAuSb2 Seo, S; Wang, Xiaoyu; Thomas, S M ...
Physical review. X,
03/2020, Volume:
10, Issue:
1
Journal Article
Peer reviewed
Open access
At ambient pressure and zero field, tetragonalCeAuSb2hosts stripe antiferromagnetic order atTN=6.3K. Here, we first show via bulk thermodynamic probes and x-ray diffraction measurements that this ...magnetic order is connected with a structural phase transition to a superstructure that likely breaksC4symmetry, thus signaling nematic order. The temperature-field-pressure phase diagram ofCeAuSb2subsequently reveals the emergence of additional ordered states under applied pressure at a multicritical point. Our phenomenological model supports the presence of a vestigial nematic phase inCeAuSb2akin to iron-based high-temperature superconductors; however, superconductivity, if present, remains to be discovered.
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We use resonant elastic x-ray scattering to determine the evolution of magnetic order in EuCd2As2 below TN=9.5 K, as a function of temperature and applied magnetic field. We find an A-type ...antiferromagnetic structure with in-plane magnetic moments, and observe dramatic magnetoresistive effects associated with field-induced changes in the magnetic structure and domain populations. Our ab initio electronic structure calculations indicate that the Dirac dispersion found in the nonmagnetic Dirac semimetal Cd3As2 is also present in EuCd2As2, but is gapped for T<TN due to the breaking of C3 symmetry by the magnetic structure.
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