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Keywords: crystal growth; crystal structure; topological band gap; topological insulators; weak topological insulators EN crystal growth crystal structure topological band gap topological insulators weak topological insulators 15342 15342 1 12/03/20 20201201 NES 201201 B Research on topological insulators (TIs) b has rapidly progressed, notably owing to their intriguing physical properties. Crystal growth, crystal structure, topological band gap, topological insulators, weak topological insulators. [Extracted from the article]

Spectroscopic detection of Dirac and Weyl fermions in real materials is vital for both, promising applications and fundamental bridge between high-energy and condensed-matter physics. While the presence of Dirac and noncentrosymmetric Weyl fermions is well established in many materials, the magnetic Weyl semimetals still escape direct experimental detection. In order to find a time-reversal symmetry breaking Weyl state we design two materials and present here experimental and theoretical evidence of realization of such a state in one of them, YbMnBi2. We model the time-reversal symmetry breaking observed by magnetization and magneto-optical microscopy measurements by canted antiferromagnetism and find a number of Weyl points. Using angle-resolved photoemission, we directly observe two pairs of Weyl points connected by the Fermi arcs. Our results not only provide a fundamental link between the two areas of physics, but also demonstrate the practical way to design novel materials with exotic properties. Candidate materials containing magnetic Weyl fermions remain rare. Here, the authors report evidence of a magnetic Weyl state and observe the surface Fermi arcs in YbMnBi2. [ABSTRACT FROM AUTHOR]

The layered ternary compound TaIrTe4 has been predicted to be a type-II Weyl semimetal with only four Weyl points just above the Fermi energy. Performing magnetotransport measurements on this material we find that the resistivity does not saturate for fields up to 70 T and follows a ρ~B1.5 dependence. Angular-dependent de Haas-van Alphen measurements reveal four distinct frequencies. Analyzing these magnetic quantum oscillations by use of density functional theory calculations we establish that in TaIrTe4 the Weyl points are located merely ~40-50 meV above the chemical potential. [ABSTRACT FROM AUTHOR]

Abstract: Na x CoO2 for x ≈0.75 is a rather unusual metal. It is an …ABAB… stack of CoO2 sheets intercalated with Na atoms. It has a large Curie–Weiss magnetic susceptibility. Neutron scattering sees spin correlations which are ferromagnetic in plane and antiferromagnetic in stack direction. Below about 22K it orders in this way with an unusual small moment of about 0.2 μ Bohr per Co atom. Its Fermi surface measured by photoemission is a cylinder around the stack axis. Density functional calculations in local spin density approximation are presented which treat the partial Na occupation in a well justified virtual crystal approximation. They provide all those findings and yield an understanding as itinerant magnetism. In addition, a ferromagnetic order also in stack direction, which is a very clear half-metall, is nearly energetically degenerate with the antiferromagnetic ground state, with dramatic Fermi surface reconstruction. This could yield a clue to the anomalous thermopower and its strong field dependence. [Copyright &y& Elsevier]

Recently, we reported [M. Wagner et al., J. Mater. Res. 26, 1886 (2011)] transport measurements on the semiconducting intermetallic system Ruln3 and its substitution derivatives RuIn3-xAx (A = Sn, Zn). Higher values of the thermoelectric figure of merit (zT = 0.45) compared to the parent compound were achieved by chemical substitution. Here, using density functional theory based calculations, we report on the microscopic picture behind the measured phenomenon. We show in detail that the electronic structure of the substitution variants of the intermetallic system Ruln3-xAx (A = Sn, Zn) changes in a rigid-band-like fashion. This behavior makes possible the fine tuning of the substitution concentration to take advantage of the sharp peaklike features in the density of states of the semiconducting parent compound. Trends in the transport properties calculated using the semiclassical Boltzmann transport equations within the constant scattering time approximation are in good agreement with the former experimental results for Ruin3-xSnx. Based on the calculated thermopower for the &rgr;-doped systems, we reinvestigated the Zn-substituted derivative and obtained ZnO-free RuIn3-xZnx. The new experimental results are consistent with the calculated trend in thermopower and yield a large zT value of 0.8. [ABSTRACT FROM AUTHOR]

In a joint experimental and theoretical study, we investigate the isostructural collapse from the ambient pressure tetragonal phase to a collapsed tetragonal phase for nonsuperconducting metallic SrFe2As2 and SrFe1.8Ru0.2As2. The crystallographic details have been studied using x-ray powder diffraction up to 20 GPa pressure in a diamond anvil cell. The structural phase transition occurs at 10 and 9 GPa for SrFe2As2 and SrFe1.8Ru0.2As2, respectively. The changes in the unit cell dimensions are highly anisotropic with a continuous decrease of the c lattice parameter with pressure, while the a-axis length increases until the transition to a collapsed tetragonal phase and then continues to decrease. Across the phase transition, we observe volume reductions of 5% and 4% for SrFe2As2 and SrFe1.8Ru0.2As2, respectively. We are able to discern that Ru substitution on the Fe site acts like "chemical pressure" to the system. Density-functional theory-based calculations of the electronic structure and electron localizability indicator are consistent with the experimental observations. Detailed analysis of the electronic structure in k space and real space reveals As 4pz interlayer bond formation as the driving force of the c/a collapse with a change in the As-As bond length of about 0.35 Å. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation‐free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well‐characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth‐based subiodides and recently succeeded in synthesizing a new compound Bi12Rh3Sn3I9, which is structurally closely related to Bi14Rh3I9 – a stable, layered material. In fact, Bi14Rh3I9 is the first experimentally supported weak 3D TI. Both structures are composed of well‐defined intermetallic layers of ∞2[(Bi4Rh)3I]2+ with topologically protected electronic edge‐states. The fundamental difference between Bi14Rh3I9 and Bi12Rh3Sn3I9 lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi14Rh3I9 are isolated by ∞1[Bi2I8]2− chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to ∞2[Sn3I8]2− layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity. [ABSTRACT FROM AUTHOR]

We report density functional theory calculations for Mo3S7(dmit)3. We derive an ab initio tight-binding model from overlaps of Wannier orbitals; finding a layered model with interlayer hopping terms ~3/4 the size of the in-plane terms. The in-plane Hamiltonian interpolates the kagomé and honeycomb lattices. It supports states localized to dodecahedral rings within the plane, which populate one-dimensional (1D) bands and lead to a quasi-1D spin-one model on a layered honeycomb lattice once interactions are included. Two lines of Dirac cones also cross the Fermi energy. [ABSTRACT FROM AUTHOR]

A correction to the article " Ferromagnetic elements by epitaxial growth: A density functional prediction" that was published in number 85, page 024407, 2012 issue is presented.

Interfacial phonons between iron-based superconductors (FeSCs) and perovskite substrates have received considerable attention due to the possibility of enhancing preexisting superconductivity. Using scanning tunneling spectroscopy, we studied the correlation between superconductivity and e-ph interaction with interfacial phonons in an iron-based superconductor Sr2VO3FeAs (Tc≈33 K) made of alternating FeSC and oxide layers. The quasiparticle interference measurement over regions with systematically different average superconducting gaps due to the e-ph coupling locally modulated by O vacancies in the VO2 layer, and supporting self-consistent momentum-dependent Eliashberg calculations provide a unique real-space evidence of the forward-scattering interfacial phonon contribution to the total superconducting pairing. [ABSTRACT FROM AUTHOR]

Motivated by recent spin- and angular-resolved photoemission (SARPES) measurements of the two-dimensional electronic states confined near the (001) surface of oxygen-deficient SrTiO3, we explore their spin structure by means of ab initio density functional theory (DFT) calculations of slabs. Relativistic nonmagnetic DFT calculations display Rashba-like spin winding with a splitting of a few meV and when surface magnetism on the Ti ions is included, bands become spin-split with an energy difference ~100 meV at the Γ point, consistent with SARPES findings. While magnetism tends to suppress the effects of the relativistic Rashba interaction, signatures of it are still clearly visible in terms of complex spin textures. Furthermore, we observe an atomic specialization phenomenon, namely, two types of electronic contributions: one is from Ti atoms neighboring the oxygen vacancies that acquire rather large magnetic moments and mostly create in-gap states; another comes from the partly polarized t2g itinerant electrons of Ti atoms lying further away from the oxygen vacancy, which form the two-dimensional electron system and are responsible for the Rashba spin winding and the spin splitting at the Fermi surface. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation-free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well-characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth-based subiodides and recently succeeded in synthesizing a new compound Bi 12 Rh 3 Sn 3 I 9 , which is structurally closely related to Bi 14 Rh 3 I 9 - a stable, layered material. In fact, Bi 14 Rh 3 I 9 is the first experimentally supported weak 3D TI. Both structures are composed of well-defined intermetallic layers of ∞ 2 [(Bi 4 Rh) 3 I] 2+ with topologically protected electronic edge-states. The fundamental difference between Bi 14 Rh 3 I 9 and Bi 12 Rh 3 Sn 3 I 9 lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi 14 Rh 3 I 9 are isolated by ∞ 1 [Bi 2 I 8 ] 2- chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to ∞ 2 [Sn 3 I 8 ] 2- layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Cs2AgF4 was proposed to be an orbitally ordered ferromagnet based on recent neutron scattering data. Here, we report a detailed electronic structure study within the local spin density approximation also including strong Coulomb repulsion U. We investigate the influence of an orthorhombic distortion of the Ag environment and the importance of the on-site Coulomb repulsion. We find good quantitative agreement with both the experimentally observed exchange coupling and structural changes. Thus, our results strongly support that Cs2AgF4 is a strongly correlated charge-transfer insulator where the ferromagnetism is driven by orbital order.