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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Topological Crystalline Insulator Candidate ErAsS with Hourglass Fermion and Magnetic-Tuned Topological Phase Transition

Topological crystalline insulators (TCIs) with hourglass fermion surface state have attracted a lot of attention and are further enriched by crystalline symmetries and magnetic order. Here, the emergence of hourglass fermion surface state and exotic phases in the newly discovered, air-stable ErAsS single crystals are shown. In the paramagnetic phase, ErAsS is expected to be a TCI with hourglass fermion surface state protected by the nonsymmorphic symmetry. Dirac-cone-like bands and nearly linear dispersions in large energy range are experimentally observed, consistent well with theoretical calculations. Below T N ≈ 3.27 K, ErAsS enters a collinear antiferromagnetic state, which is a trivial insulator breaking the time-reversal symmetry. An intermediate incommensurate magnetic state appears in a narrow temperature range (3.27–3.65 K), exhibiting an abrupt change in magnetic coupling. Overall, the results reveal that ErAsS is an experimentally available TCI candidate and provide a unique platform to understand the formation of hourglass fermion surface state and explore magnetic-tuned topological phase transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ErAsS by Materials Project

ErAsS is Matlockite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Er3+ is bonded in a 9-coordinate geometry to four equivalent As1- and five equivalent S2- atoms. There are a spread of Er–As bond distances ranging from 3.10–3.15 Å. There are four shorter (2.79 Å) and one longer (2.83 Å) Er–S bond lengths. As1- is bonded in a 8-coordinate geometry to four equivalent Er3+ and four equivalent As1- atoms. There are two shorter (2.55 Å) and two longer (2.85 Å) As–As bond lengths. S2- is bonded to five equivalent Er3+ atoms to form a mixture of distorted corner and edge-sharing SEr5 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ErAsSe by Materials Project

ErAsSe is Matlockite structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Er3+ is bonded in a 9-coordinate geometry to four equivalent As1- and five equivalent Se2- atoms. There are a spread of Er–As bond distances ranging from 3.06–3.15 Å. There are a spread of Er–Se bond distances ranging from 2.88–3.02 Å. As1- is bonded in a 8-coordinate geometry to four equivalent Er3+ and four equivalent As1- atoms. There are a spread of As–As bond distances ranging from 2.57–2.94 Å. Se2- is bonded in a 5-coordinate geometry to five equivalent Er3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ErAsSe by Materials Project

ErAsSe crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Er3+ is bonded in a 9-coordinate geometry to four equivalent As1- and five equivalent Se2- atoms. There are a spread of Er–As bond distances ranging from 3.06–3.15 Å. There are a spread of Er–Se bond distances ranging from 2.88–3.02 Å. As1- is bonded in a 8-coordinate geometry to four equivalent Er3+ and four equivalent As1- atoms. There are two shorter (2.58 Å) and two longer (2.95 Å) As–As bond lengths. Se2- is bonded in a 5-coordinate geometry to five equivalent Er3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The eROSITA Final Equatorial-Depth Survey (eFEDS)

The eROSITA Final Equatorial Depth Survey (eFEDS), completed in survey mode during the calibration and performance verification phase of the eROSITA instrument on Spectrum Roentgen Gamma, delivers data at and beyond the final depth of the 4-yr eROSITA all-sky survey (eRASS:8), f 0.5–2 keV = 1.1 × 10 –14 erg s –1 cm –2 , over 140 deg 2 . It provides the first view of normal galaxy X-ray emission from X-ray binaries (XRBs) and the hot interstellar medium at the full depth of eRASS:8. We used the Heraklion Extragalactic Catalogue (HECATE) of galaxies to correlate with eFEDS X-ray sources and identify X-ray detected normal galaxies. This flux-limited X-ray survey is relatively free from selection effects and enables the study of integrated normal galaxy X-ray emission and its relation to galaxy parameters such as the stellar mass, star formation rate (SFR), and metallicity. We cross-correlated 32 646 eFEDS X-ray sources to 1181 HECATE normal galaxies and obtained 94 matches. We classified galaxies as star-forming, early-type, composite, and active galactic nuclei (AGN) using Sloan Digital Sky Survey (SDSS) and Six-degree Field (6dF) optical spectroscopy. The eFEDS field harbours 37 normal galaxies: 36 late-type (star-forming) galaxies and one early-type galaxy. There are 1.9 times as many normal galaxies as predicted by scaling relations via simulations, with an overabundance of late-type galaxies and a dearth of early-type galaxies. When compared with empirical relations, eFEDS dwarf galaxies with a high specific SFR have elevated L X /SFR at a fixed specific SFR and metallicity, indicating an increase in XRB emission due to low metallicity. We expect that eRASS:8 will detect 12 500 normal galaxies, the majority of which will be star-forming, with the caveat that there are unclassified sources in eFEDS and galaxy catalogue incompleteness issues that could increase the actual number of detected galaxies over these current estimates. eFEDS observations detected a rare population of galaxies – the metal-poor dwarf starbursts – that do not follow known scaling relations. eRASS is expected to discover significant numbers of these high-redshift analogues, which are important for studying the heating of the intergalactic medium at high redshift. Further investigation of the hot gas emission from normal galaxies and stochastic effects in the dwarf galaxy population are required to constrain their X-ray output.

79 ASTRONOMY AND ASTROPHYSICS↗