[en] Optical phonons are employed to probe a structural phase transition of IrTe_2−xSe_x at T_C∼280 K for x = 0 and T_C∼491 K for x = 0.45, which is dictated by Ir dimerization with charge modulations. Phonon Raman spectra show a discontinuous change at T_C and thermal hysteresis. A 165 cm⁻¹ A_g mode involving out-of-plane motions of Te atoms is mostly affected by Se doping. This highlights the role of interlayer Te–Te interactions in inducing the structural instability. For temperatures below T_C both x = 0 and x = 0.45 compounds exhibit commonly five zone-folded peaks for the 128 cm⁻¹ E_g in-plane mode and six zone-folded peaks for the 165 cm⁻¹ A_g mode. This is taken as a signature of a respective quintupling and sextupling of the unit cell. Our results, on the one hand, are consistent with a 1/5 charge modulation reported by previous studies and, on the other hand, indicate that the ground state of IrTe_2−xSe_x lies in proximity to a 1/6 commensurate charge modulation phase. (paper)

[en] Crystallochemical analysis of compounds containing IrX_n polyhedra (X O, S, Se, Te) within their structure was carried out using the Voronoi-Dirichlet division and method of intersecting spheres. It was ascertained that for iridium atoms, their oxidation degree varying from III to VI, octahedral coordination by chalcogen atoms is characteristic. Iridium atoms of Ir^IVO₄ squares and Ir^IVO₆, Ir^VO₆, Ir^IIITe₆ octahedrons can form additional Ir-M bonds (M = Li, Na, K, Cs, Ca, Sr, Cu, Ta), whereas in the structure of oxygen-containing compounds Ir(III) and Ir(VI) there are no Ir-M direct interactions. Influence of Ir atoms site-symmetry and valency state on characteristics of their Voronoi-Dirichlet polyhedrons and character of IrX₆ octahedron distortion were considered

[en] We have investigated the electronic states of IrTe₂ by using angle-resolved photoemission spectroscopy to elucidate the origin of the structural phase transition. Both the Ir 4f and Te 4d core level spectra exhibit dramatic splitting below the phase transition temperature T_s, suggesting that there exist two inequivalent Ir and Te sites with distinctly different electronic states in the distorted phase. The band related to the saddle points at the Fermi level (E_F) is strongly reconstructed, which removes the van Hove singularity from E_F below T_s. The wavevector connecting the adjacent saddle points is consistent with the in-plane superstructure modulation wavevector. These results indicate that the phase transition in IrTe₂ is intimately associated with the saddle points. As the van Hove singularity mainly originates from the Te p_x+p_y orbitals, the Te 5p electronic states play a dominant role in the structural phase transition. (paper)

[en] Bulk iridium ditelluride (IrTe₂) is a layered material and is known for its interesting electronic and structural properties, such as large spin–orbit coupling, charge ordering, and superconductivity. However, so far there is no experimental study about the fabrication of monolayer IrTe₂. Here we report the formation of IrTe₂ monolayer on Ir(111) substrate by direct tellurization method. Scanning tunneling microscope (STM) images show the coexistence of 1/5 phase and 1/6 phase structures of IrTe₂ at room temperature. We also obtained STM images showing distorted stripe feature under low temperatures. This stripe feature is possibly induced by the strain between the IrTe₂ monolayer and the metal substrate. Density functional theory (DFT) calculations show that the IrTe₂ monolayer has strong interaction with the underlying Ir(111) substrate. (rapid communication)

[en] Angle-resolved photoemission spectroscopy is performed to study the bulk and surface electronic structures of non-superconducting IrTe₂ and superconducting Pt_0.05Ir_0.95Te₂. In addition to the bulk electronic bands predicted by the local density approximation calculations, we observe two Dirac cone-like bands at the Brillouin zone center, which are non-dispersive along k_z, suggesting that the extra bands are surface state bands. As the experimental results are well consistent with the ab initio calculations of surface states, the parity analysis proves that these surface state bands are topologically trivial and thus exclude (Pt_xIr_1-x)Te₂ as a possible topological superconductor candidate. (authors)

[en] The resistivity and magnetization for the CuIr₂(S_1−xTe_x)₄ (0 = ≤ × ≤ 0.10) system are investigated. Compared with the Se doping, the substitution of Te for S leads to stronger suppression on the metal-insulator transition. Vacancies and imperfections in the sample lattice are found to modify the magnetization, which can be qualitatively understood to consist of the Pauli paramagnetism, Landau diamagnetism, Larmor diamagnetism and Curie magnetism contributions. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

No abstract available

[en] The prevalent global energy crisis calls for searching viable pathways for generating green hydrogen as an alternative energy resource. Dye-sensitized photocatalytic water splitting is a feasible solution to produce green hydrogen. However, identifying suitable catalysts has been one of the bottlenecks in driving dye-sensitized photocatalysis efficiently. In this work, a new class of electrocatalysts is reported based on the layered Weyl semimetals MIrTe${}_4$ (M = Nb, Ta) for the Eosin Y (EY)-sensitized hydrogen evolution reaction (HER). NbIrTe${}_4$ and TaIrTe${}_4$ exhibit HER activities of ≈18 000 and 14 000 µmol g${}^{-<!--\; ???\; -->1}$ respectively, after 10 h of irradiation with visible light. Time-dependent UV-Vis spectroscopy and high-pressure liquid chromatography coupled with mass spectrometry analysis shed light on the reaction dynamics and enable a deeper understanding of the observed trend in hydrogen evolution rates for MIrTe${}_4$. MIrTe${}_4$ semimetals outperform transition metal-based Weyl semimetals in terms of catalytic HER activity using EY as photosensitizer and triethanolamine as the sacrificial agent. It is hypothesized that the topology-related band inversion in MIrTe${}_4$ Weyl semimetals promotes a high density of M d-states near the Fermi level, driving their high catalytic performance. This study introduces a new class of layered Weyl semimetals as efficient catalysts, and provides perspectives for designing topology-enhanced catalysts. (© 2023 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)

[en] Arsenic and tellurium exhibit a variety of chemical bonds depending on valence states. Examples include As zigzag chains in CaFeAs_2, As_2 dimers in CaFe_2As_2, Ir_2 dimers in IrTe_2, and Te_2 dimers in AuTe_2, which exhibit superconductivity when the dimers are broken by chemical doping. (author)

[en] Highlights: • We performed STS measurements on patchwork structure in Ir_0_._9_3Pt_0_._0_7Te_2. • Patchwork structure has similar electronic features to those of IrTe_2. • Patchwork structure is caused by strain due to the dopant Pt. - Abstract: We report on the scanning tunneling microscopy (STM) and spectroscopy (STS) study on a newly discovered superconductor, Ir_1_−_xPt_xTe_2. We previously found that the sample which shows superconductivity forms so called “patchwork structure (PS)”. To obtain the spatial evolution of electronic structure on the PS, we performed STM/STS measurements on the PS. STS measurements revealed that an averaged spectrum shows the same energy asymmetry as that in the low temperature phase in the parent material, IrTe_2. Furthermore, the spectrum at the trough on the PS is more asymmetric than that at the crest. This tendency is similar to that observed on the supermodulation in the low temperature phase in IrTe_2.