Phase stability and electronic structure of iridium metal at the megabar range

[EN] The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.The authors thank the financial support of the Spanish Ministry of Science, Innovation and Universities, the Spanish Research Agency (AEI), the European Fund for Regional Development (FEDER) under Grant No. MAT2016-75586-C4-1/2-P and the Generalitat Valenciana under Grant Prometeo/2018/123 (EFIMAT). V. M. acknowledges the Juan de la Cierva fellowship (FJCI-2016-27921) and J.A.S. acknowledges the Ramón y Cajal fellowship program (RYC-2015-17482) and Spanish Mineco Project FIS2017-83295-P. We acknowledge the European Synchrotron Radiation Facility for provision of official research beamtimes, the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No 2009 00971), Knut and Alice Wallenbergs Foundation Project Strong Field Physics and New States of Matter CoTXS (2014 2019). The interpretation of theoretical results was supported by the Ministry of Science and High Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST MISIS (No. K2-2019-001) implemented by a governmental decree dated 16 March 2013, No 211.Monteseguro, V.; Sans-Tresserras, JÁ.; Cuartero, V.; Cova, F.; Abrikosov, I.; Olovsson, W.; Popescu, C.... (2019). Phase stability and electronic structure of iridium metal at the megabar range. Scientific Reports. 9:1-9. https://doi.org/10.1038/s41598-019-45401-xS199Cynn, H., Klepeis, J. E., Yoo, C.-S. & Young, D. A. 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Al L-2,L-3 edge x-ray absorption spectra in III-V semiconductors: Many-body perturbation theory in comparison with experiment

We investigate core excitations of the Al 2p edge in the III-V semiconductors AlP, AlAs, AlSb, and AlN. For the latter, we consider the wurtzite, zinc-blende, and rock-salt polymorphs. First-principles calculations are performed utilizing two different approaches, which are the solution of the Bethe-Salpeter equation (BSE) as well as the supercell technique employing the core-hole approximation. In addition, measurements of the electron energy-loss near-edge structure of the metastable AlN phase are presented. We find that the relative intensities of the spectral features are better described by the BSE than by the supercell method. We analyze the character of the near-edge peaks and trace back their origin to strongly bound core excitons in the case of AlSb and rock-salt AlN