39 research outputs found
Spectromicroscopy of electronic phase separation in KFeSe superconductor
Structural phase separation in AFeSe system has been studied
by different experimental techniques, however, it should be important to know
how the electronic uniformity is influenced, on which length scale the
electronic phases coexist, and what is their spatial distribution. Here, we
have used novel scanning photoelectron microscopy (SPEM) to study the
electronic phase separation in KFeSe, providing a direct
measurement of the topological spatial distribution of the different electronic
phases. The SPEM results reveal a peculiar interconnected conducting
filamentary phase that is embedded in the insulating texture. The filamentary
structure with a particular topological geometry could be important for the
high T superconductivity in the presence of a phase with a large magnetic
moment in AFeSe materials.Comment: 14 pages,3 figure
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North Atlantic Paleoceanography: The Last Five Million Years
In the North Atlantic, cold, relatively salty water sinks in the icy Labrador and Greenland seas, forming North Atlantic Deep Water (NADW). This circulates through the global ocean, driving ocean overturning and global heat transport and, thus, impacting global climate. As one of the most climatically sensitive regions on Earth, the North Atlantic has experienced abrupt changes to its ocean-atmosphere-cryosphere system, triggered by fluctuations in meltwater delivery to source areas of NADW formation. For about the past 100 thousand years, these abrupt jumps in climate state have manifested as ‘Dansgaard/Oeschger’ (D/O) oscillations (millennial-scale warm-cold oscillations) and ‘Heinrich’ events in ice and marine sediment cores, respectively [e.g., Dansgaard et al.,1993; Bond and Lotti, 1995]. These Heinrich events are characterized as huge input of ice-rafted debris (IRD) and meltwater pulses, documenting episodes of sudden instability and collapse of the current Greenland ice sheets and the Laurentide ice sheet, the latter of which covered northern North America several times during the Pleistocene Epoch
Pebbles and sand on asteroid (162173) Ryugu: In situ observation and particles returned to Earth
International audienceThe Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu’s boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid
Electronic structure and phase separation of superconducting and nonsuperconducting KxFe2-ySe2 revealed by x-ray photoemission spectroscopy
We have investigated the electronic structure of superconducting (SC) and nonsuperconducting (non-SC) KxFe2-ySe2 using x-ray photoemission spectroscopy (XPS). The spectral shape of the Fe 2p XPS is found to depend on the amount of Fe vacancies. The Fe 2p(3/2) peak of the SC and non-SC Fe-rich samples is accompanied by a shoulder structure on the lower binding energy side, which can be attributed to the metallic phase embedded in the Fe2+ insulating phase. The absence of the shoulder structure in the non-SC Fe-poor sample allows us to analyze the Fe 2p spectra using a FeSe4 cluster model. The Fe 3d-Se 4p charge-transfer energy of the Fe2+ insulating phase is found to be similar to 2.3 eV which is smaller than the Fe 3d-Fe 3d Coulomb interaction of similar to 3.5 eV. This indicates that the Fe2+ insulating state is the charge-transfer type in the Zaanen-Sawatzky-Allen scheme. We also find a substantial change in the valence-band XPS as a function of Fe content and temperature. The metallic state at the Fermi level is seen in the SC and non-SC Fe-rich samples and tends to be enhanced with cooling in the SC sample