Superconductivity in Ca10(Ir4As8)(Fe2As2)5 with Square-Planar Coordination of Iridium

Abstract

We report the unprecedented square-planar coordination of iridium in the iron iridium arsenide Ca 10 (Ir 4 As 8 )(Fe 2 As 2 ) 5 . This material experiences superconductivity at 16 K. X-ray photoemission spectroscopy and first-principles band calculation suggest Ir(II) oxidation state, which yields electrically conductive Ir 4 As 8 layers. Such metallic spacer layers are thought to enhance the interlayer coupling of Fe 2 As 2 , in which superconductivity emerges, thus offering a way to control the superconducting transition temperature.

Coexistence of Bloch electrons and glassy electrons inCa10(Ir4As8)(Fe2−xIrSawada1, Ootsuki2, Kudo3 et al. 2014Phys. Rev. B6070View full textAdd to dashboardCite

“…[12] In contrast, the intensity of the region from 2 eV to 4 eV below E F does not depend appreciably on the photon energy. The valence-band spectra are basically consistent with the density of states calculated by Kudo et al [10] The calculation indicates that the structure near E F is dominated by the Fe 3d orbitals with a mixture of the Ir 5d e g orbitals, consistent with the Fe 3p-3d resonance. On the other hand, the structures ranging from 2 eV to 4 eV below E F can be assigned to the Ir 5d t 2g orbitals which are mixed with the Fe 3d orbitals.…”

“…Isostructural Ca 10 (Ir 4 As 8 )(Fe 2−x Ir x As 2 ) 5 is another member of the iron-based superconductors with T c = 16 K. [10] This material has square-planer Ir 4 As 8 layers, which are isotypic to the Pt 4 As 8 layers in Ca 10 (Pt 4 As 8 )(Fe 2−x Pt x As 2 ) 5 . The band-structure calculation for Ca 10 (Ir 4 As 8 )(Fe 2−x Ir x As 2 ) 5 predicts that the Ir 5d orbitals have relatively large contribution to the density of states at E F compared to Ca 10 (Pt 4 As 8 )(Fe 2−x Pt x As 2 ) 5 .…”

“…The band-structure calculation for Ca 10 (Ir 4 As 8 )(Fe 2−x Ir x As 2 ) 5 predicts that the Ir 5d orbitals have relatively large contribution to the density of states at E F compared to Ca 10 (Pt 4 As 8 )(Fe 2−x Pt x As 2 ) 5 . [10] In addition, a recent x-ray diffraction study by Sugawara et al has reported doubling of the unit cell along the c-axis below 100 K which is attributed to the Ir 5d orbital crossover. [11] In this context, an ARPES study on Ca 10 (Ir 4 As 8 )(Fe 2−x Ir x As 2 ) 5 is highly interesting and important in order to reveal electronic structure of the Ir 4 As 8 layer as well as its impact on the FeAs layer.…”

“…[10] The lattice constants a and c are ∼ 8.725Å and 20.70Å around 20 K [11]. The ARPES measurements were performed at beamline 28A of Photon Factory, KEK using a SCIENTA SES-2002 electron analyzer with circularly polarized light.…”

Superconductivity by transition metal doping in Ca10(Fe1−xMxAs)10(Pt3As8) (M= Co, Ni, Cu)

“…In 2011 the new superconductors Ca 10 (Fe 1−x Pt x As) 10 (Pt 3 As 8 ) (1038 phase, space group P 1) and polymorphic Ca 10 (FeAs) 10 (Pt 4 As 8 ) (1048-phases, space groups P 4/n, P 2 1 /n, P 1) with critical temperatures up to 35 K were discovered [15][16][17]. This new class recently expanded by analogous compounds with iridium (Ir1048) [18] and palladium (Pd1038) [19] instead of platinum. Due to the presence of the second metal pnictide layer Pt z As 8 (z = 3, 4) next to FeAs, as well as the low symmetry of these compounds (space group P 1) they were initially considered as rather peculiar representatives of the iron arsenide family.…”