Electronic and crystal structures of Ln FeAsO1- xHx(Ln= La, Sm) studied by x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction: II pressure dependence

Yoshiya Yamamoto; Hitoshi Yamaoka; Takuma Kawai; Masahiro Yoshida; Jun-Ichi Yamaura; Kenji Ishii; Seiichiro Onari; Takayuki Uozumi; Atsushi Hariki; Munetaka Taguchi; Kensuke Kobayashi; Jung-Fu Lin; Nozomu Hiraoka; Hirofumi Ishii; Ku-Ding Tsuei; Hiroshi Okanishi; Soshi Iimura; Satoru Matsuishi; Hideo Hosono; Jun'ichiro Mizuki

doi:10.1088/1361-648X/abfaf4

Electronic and crystal structures of Ln FeAsO_{1- x}H_x(Ln= La, Sm) studied by x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction: II pressure dependence

J Phys Condens Matter. 2021 May 28;33(25). doi: 10.1088/1361-648X/abfaf4.

Authors

Yoshiya Yamamoto¹, Hitoshi Yamaoka², Takuma Kawai¹, Masahiro Yoshida¹, Jun-Ichi Yamaura³, Kenji Ishii⁴, Seiichiro Onari⁵, Takayuki Uozumi⁶, Atsushi Hariki⁶, Munetaka Taguchi⁷, Kensuke Kobayashi⁸, Jung-Fu Lin⁹, Nozomu Hiraoka¹⁰, Hirofumi Ishii¹⁰, Ku-Ding Tsuei¹⁰, Hiroshi Okanishi¹¹, Soshi Iimura¹¹, Satoru Matsuishi¹¹, Hideo Hosono^{3

11}, Jun'ichiro Mizuki¹

Affiliations

¹ Graduate School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan.
² RIKEN SPring-8 Center, Sayo, Hyogo 679-5148, Japan.
³ Materials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan.
⁴ Synchrotron Radiation Research Center, National Institutes for Quantum and Radiological Science and Technology, Hyogo 679-5148, Japan.
⁵ Department of Physics, Nagoya University, Chikusa, Nagoya 464-8602, Japan.
⁶ Department of Physics and electronics, Osaka Prefecture University, 1-1 Gakuen, Nakaku, Sakai, Osaka 599-8531, Japan.
⁷ Toshiba Nanoanalysis Corporation, Kawasaki, Kanagawa 212-8583, Japan.
⁸ Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan.
⁹ Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, United States of America.
¹⁰ National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
¹¹ Laboratory for Materials and Structures, Tokyo Institute of Technology, Yokohama 226-8503, Japan.

PMID: 33890871
DOI: 10.1088/1361-648X/abfaf4

Abstract

We examine electronic and crystal structures of iron-based superconductorsLnFeAsO_1-xH_x(Ln= La, Sm) under pressure by means of x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), and x-ray diffraction. In LaFeAsO the pre-edge peak on high-resolution XAS at the Fe-Kabsorption edge gains in intensity on the application of pressure up to 5.7 GPa and it saturates in the higher pressure region. We found integrated-absolute difference values on XES forLn= La, corresponding to a spin state, decline on the application of pressure, and then it is minimized when theT_capproaches the maximum at around 5 GPa. In contrast, such the optimum value was not detected forLn= Sm. We reveal that the superconductivity is closely related to the lower spin state forLn= La unlike Sm case. We observed that As height from the Fe basal plane and As-Fe-As angle on the FeAs₄tetrahedron forLn= La deviate from the optimum values of the regular tetrahedron in superconducting (SC) phase, which has been widely accepted structural guide to SC thus far. In contrast, the structural parameters were held near the optimum values up to ∼15 GPa forLn= Sm.

Keywords: crystal structure; electronic structure; high pressure; iron superconductors; pnictides and chalcogenides; x-ray absorption spectra; x-ray diffraction.