Unconventional Metal Research Articles

The modified alpha power law based model of statistical fluctuation in nanometer FGMOSFET

The modified alpha power law based model of statistical fluctuation in drain current of an unconventional Metal Oxide Semiconductor Field Effect Transistor namely Floating-Gate Metal Oxide Semicond...

Local Environment of Terbium(III) Ions in Layered Nanocrystalline Zirconium(IV) Phosphonate-Phosphate Ion Exchange Materials.

The structures of Zr(IV) phosphonate-phosphate based, unconventional metal organic framework materials have been determined using atomic pair distribution function analysis of high energy, X-ray total scattering diffraction data. They are found to form as nanocrystalline layers of Zr phosphate, similar to the bulk, but with a high degree of interlayer disorder and intermediate intralayer order extending around 5 nm. These materials are of interest for their high selectivity for 3+ lanthanide ions. To investigate the mechanism of the selectivity, we utilize difference pair distribution function analysis to extract the local structural environment of Tb3+ ions loaded into the framework. The ions are found to sit between the layers in a manner resembling the local environment of Tb in Scheelite-type terbium phosphate. By mapping this local structure onto that of the refined structure for zirconium-phenyl-phosphonate, we show how dangling oxygens from the phosphate groups, acting like nose hairs, are able to reorient to provide a friendly intercalation environment for the Tb3+ ions.

Influence of molybdenum oxide on structural, optical and physical properties of oxychloride glasses for nonlinear optical devices

Abstract The unconventional Heavy Metal Oxide Glasses (HMOG) are characterized by a low phonon energy, large infrared range transmission, high refractive index and nonlinear optical properties. Ternary glasses have been synthesized and studied in the Sb 2 O 3 – MoO 3 -ZnCl 2 system. Further, the glass formation compositional limits are reported and some glass samples with the formula: (90-x)Sb 2 O 3 -xMoO 3 –10 ZnCl 2 (10 ≤ x ≤ 50, mole%) were elaborated. Thermal properties have been measured and indicating that the glass transition temperature decreases with increasing proportions of molybdenum oxide. The evolution of density, microhardness and elastic modulus has been studied as functions of parameter x and Raman spectra measurements have been shown the partial conversion of MoO 6 octahedral units into MoO 4 tetrahedral.

Spin-freezing perspective on cuprates

The high-temperature superconducting state in cuprates appears if charge carriers are doped into a Mott insulating parent compound. An unresolved puzzle is the unconventional nature of the normal state above the superconducting dome, and its connection to the superconducting instability. At weak hole-doping, a "pseudo-gap" metal state with signatures of time-reversal symmetry breaking is observed, which near optimal doping changes into a "strange metal" with non-Fermi liquid properties. Qualitatively similar phase diagrams are found in multi-orbital systems, such as pnictides, where the unconventional metal states arise from a Hund coupling induced spin-freezing. Here, we show that the relevant model for cuprates, the single-orbital Hubbard model on the square lattice, can be mapped onto an effective multi-orbital problem with strong ferromagnetic Hund coupling. The spin-freezing physics of this multi-orbital system explains the phenomenology of cuprates, including the pseudo-gap, the strange metal, and the d-wave superconducting instability. Our analysis suggests that spin-freezing is the universal mechanism which controls the properties of unconventional superconductors.

Unconventional high-Tc superconductivity in fullerides.

A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter-the overlap between the outer wave functions of the constituent molecules-is controlled by the C60 (3-) molecular electronic structure via the on-molecule Jahn-Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott-Jahn-Teller state through chemical or physical pressurization yields an unconventional Jahn-Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen-Cooper-Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn-Teller and Fermi liquid metal when the Jahn-Teller distortion melts.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

Pinball liquid phase from Hund's coupling in frustrated transition-metal oxides

The interplay of nonlocal Coulomb repulsion and Hund's coupling in the $d$-orbital manifold in frustrated triangular lattices is analyzed by a multiband extended Hubbard model. We find a rich phase diagram with several competing phases, including a robust pinball liquid phase, which is an unconventional metal characterized by threefold charge order, bad metallic behavior, and the emergence of high-spin local moments. Our results naturally explain the anomalous charge-ordered metallic state observed in the triangular layered compound ${\mathrm{AgNiO}}_{2}$. The potential relevance to other triangular transition-metal oxides is discussed.

Origin and Evolution of Water Oxidation before the Last Common Ancestor of the Cyanobacteria.

Photosystem II, the water oxidizing enzyme, altered the course of evolution by filling the atmosphere with oxygen. Here, we reconstruct the origin and evolution of water oxidation at an unprecedented level of detail by studying the phylogeny of all D1 subunits, the main protein coordinating the water oxidizing cluster (Mn4CaO5) of Photosystem II. We show that D1 exists in several forms making well-defined clades, some of which could have evolved before the origin of water oxidation and presenting many atypical characteristics. The most ancient form is found in the genome of Gloeobacter kilaueensis JS-1 and this has a C-terminus with a higher sequence identity to D2 than to any other D1. Two other groups of early evolving D1 correspond to those expressed under prolonged far-red illumination and in darkness. These atypical D1 forms are characterized by a dramatically different Mn4CaO5 binding site and a Photosystem II containing such a site may assemble an unconventional metal cluster. The first D1 forms with a full set of ligands to the Mn4CaO5 cluster are grouped with D1 proteins expressed only under low oxygen concentrations and the latest evolving form is the dominant type of D1 found in all cyanobacteria and plastids. In addition, we show that the plastid ancestor had a D1 more similar to those in early branching Synechococcus. We suggest each one of these forms of D1 originated from transitional forms at different stages toward the innovation and optimization of water oxidation before the last common ancestor of all known cyanobacteria.

A fatigue design concept for metal injection molded components of 100Cr6

The fatigue behavior of rolled and machined high‐strength steel parts shows dependency on the size of material defects. In this work, the fatigue behavior of high‐strength steel specimens manufactured by Metal Injection Molding (MIM) process is investigated. Herein prealloyed 100Cr6 powder is used as base material and is sintered to 98.7% and to 95.2% relative density respectively. In order to avoid burrs resulting from the mold parting, an unconventional metal injection molding‐specific specimen shape is designed to perform experiments at notched and unmachined specimens, especially to assess the behavior of this material in component‐near conditions. Fatigue tests under axial loading with a load ratio of R = 0.1 were conducted with such specimens in martensitic condition. SEM analyses reveal that cracks originate from metal injection molding‐specific material discontinuities which can be seen as defects to this high strength steel. It was observed that irregularities at the surface, like surface roughness, open pores and locally melted surface areas lead to early fracture whereas defects in the volume, like non‐metallic inclusions lead to late fracture. Fracture mechanic analyses reveal that Murakami's short crack model is applicable to the 100Cr6 metal injection molding materials and therefore allows estimating the fatigue strength at N = 107 cycles of the metal injection molding‐material. Considering a weakest‐link approach, the fatigue strength at N = 107 cycles of the notched specimens can be well estimated using finite element modeling and the size distributions of the crack originating defects.

Ultracold fermions in a one-dimensional bipartite optical lattice: Metal-insulator transitions driven by shaking

We describe the behavior of a system of fermionic atoms loaded in a bipartite one-dimensional optical lattice that is under the action of an external time-periodic driving force. By using Floquet theory, an effective model with renormalized hopping coefficients is derived. The insulating behavior characterizing the system at half-filling in the absence of driving is dynamically suppressed and for particular values of the driving parameter the system becomes either a standard metal or an unconventional metal with four Fermi points. We use the bosonization technique to investigate the effect of on-site Hubbard interactions on the four Fermi-point metal-insulator phase transition. Attractive interactions are expected to enlarge the regime of parameters where the unconventional metallic phase arises, whereas repulsive interactions reduce it. This metallic phase is known to be a Luther-Emery liquid (spin gapped metal) for both, repulsive and attractive interactions, contrarily to the usual Hubbard model which exhibits a Mott insulator phase for repulsive interactions. Ultracold fermions in driven one-dimensional bipartite optical lattices provide an interesting platform for the realization of this long studied four Fermi-point unconventional metal.

Composite Operator Method Analysis of the Underdoped Cuprates Puzzle

The microscopical analysis of the unconventional and puzzling physics of the underdoped cuprates, as carried out lately by means of the composite operator method (COM) applied to the 2D Hubbard model, is reviewed and systematized. The 2D Hubbard model has been adopted as it has been considered the minimal model capable of describing the most peculiar features of cuprates held responsible for their anomalous behavior. COM is designed to endorse, since its foundation, the systematic emergence in any SCS of new elementary excitations described by composite operators obeying noncanonical algebras. In this case (underdoped cuprates—2D Hubbard model), the residual interactions—beyond a 2-pole approximation—between the new elementary electronic excitations, dictated by the strong local Coulomb repulsion and well described by the two Hubbard composite operators, have been treated within the noncrossing approximation. Given this recipe and exploiting the few unknowns to enforce the Pauli principle content in the solution, it is possible to qualitatively describe some of the anomalous features of high-Tc cuprate superconductors such as large versus small Fermi surface dichotomy, Fermi surface deconstruction (appearance of Fermi arcs), nodal versus antinodal physics, pseudogap(s), and kinks in the electronic dispersion. The resulting scenario envisages a smooth crossover between an ordinary weakly interacting metal sustaining weak, short-range antiferromagnetic correlations in the overdoped regime to an unconventional poor metal characterized by very strong, long-but-finite-range antiferromagnetic correlations leading to momentum-selective non-Fermi liquid features as well as to the opening of a pseudogap and to the striking differences between the nodal and the antinodal dynamics in the underdoped regime.

The Potential and Application Areas of Forging Aided by Shear Stress

The paper demonstrates the potential of unconventional metal forming method that consists in introducing shear stress at the die/workpiece interface during compression. In practice it can be realized by induction of reciprocating, vertical motion of a punch that adheres strongly to a workpiece. To estimate an effect of the method on the material flow, a relevant finite element model has been developed and the selected results of numerical simulations are presented in the paper. In comparison to the conventional forging, forming aided by shear stress is able to provide a number of benefits such as significant increase of local strains, lower press loads and the opportunity to control the strain distribution in the workpiece volume. Perspectives for continuation of the studies as well as possible application areas of forging aided by shear stress are discussed in the summary.

Anisotropic breakdown of Fermi liquid quasiparticle excitations in overdoped La2−xSrxCuO4

High-temperature superconductivity emerges from an un-conventional metallic state. This has stimulated strong efforts to understand exactly how Fermi liquids breakdown and evolve into an un-conventional metal. A fundamental question is how Fermi liquid quasiparticle excitations break down in momentum space. Here we show, using angle-resolved photoemission spectroscopy, that the Fermi liquid quasiparticle excitations of the overdoped superconducting cuprate La1.77Sr0.23CuO4 is highly anisotropic in momentum space. The quasiparticle scattering and residue behave differently along the Fermi surface and hence the Kadowaki-Wood's relation is not obeyed. This kind of Fermi liquid breakdown may apply to a wide range of strongly correlated metal systems where spin fluctuations are present.

Thio Effects and an Unconventional Metal Ion Rescue in the Genomic Hepatitis Delta Virus Ribozyme

Metal ion and nucleobase catalysis are important for ribozyme mechanism, but the extent to which they cooperate is unclear. A crystal structure of the hepatitis delta virus (HDV) ribozyme suggested that the pro-RP oxygen at the scissile phosphate directly coordinates a catalytic Mg(2+) ion and is within hydrogen bonding distance of the amine of the general acid C75. Prior studies of the genomic HDV ribozyme, however, showed neither a thio effect nor metal ion rescue using Mn(2+). Here, we combine experiment and theory to explore phosphorothioate substitutions at the scissile phosphate. We report significant thio effects at the scissile phosphate and metal ion rescue with Cd(2+). Reaction profiles with an SP-phosphorothioate substitution are indistinguishable from those of the unmodified substrate in the presence of Mg(2+) or Cd(2+), supporting the idea that the pro-SP oxygen does not coordinate metal ions. The RP-phosphorothioate substitution, however, exhibits biphasic kinetics, with the fast-reacting phase displaying a thio effect of up to 5-fold and the slow-reacting phase displaying a thio effect of ~1000-fold. Moreover, the fast- and slow-reacting phases give metal ion rescues in Cd(2+) of up to 10- and 330-fold, respectively. The metal ion rescues are unconventional in that they arise from Cd(2+) inhibiting the oxo substrate but not the RP substrate. This metal ion rescue suggests a direct interaction of the catalytic metal ion with the pro-RP oxygen, in line with experiments with the antigenomic HDV ribozyme. Experiments without divalent ions, with a double mutant that interferes with Mg(2+) binding, or with C75 deleted suggest that the pro-RP oxygen plays at most a redundant role in positioning C75. Quantum mechanical/molecular mechanical (QM/MM) studies indicate that the metal ion contributes to catalysis by interacting with both the pro-RP oxygen and the nucleophilic 2'-hydroxyl, supporting the experimental findings.

Universal sheet resistance and revised phase diagram of the cuprate high-temperature superconductors

Upon introducing charge carriers into the copper-oxygen sheets of the enigmatic lamellar cuprates, the ground state evolves from an insulator to a superconductor and eventually to a seemingly conventional metal (a Fermi liquid). Much has remained elusive about the nature of this evolution and about the peculiar metallic state at intermediate hole-carrier concentrations (p). The planar resistivity of this unconventional metal exhibits a linear temperature dependence (ρ ∝ T) that is disrupted upon cooling toward the superconducting state by the opening of a partial gap (the pseudogap) on the Fermi surface. Here, we first demonstrate for the quintessential compound HgBa2CuO4+δ a dramatic switch from linear to purely quadratic (Fermi liquid-like, ρ ∝ T(2)) resistive behavior in the pseudogap regime. Despite the considerable variation in crystal structures and disorder among different compounds, our result together with prior work gives insight into the p-T phase diagram and reveals the fundamental resistance per copper-oxygen sheet in both linear (ρ = A1T) and quadratic (ρ = A2T(2)) regimes, with A1 ∝ A2 ∝ 1/p. Theoretical models can now be benchmarked against this remarkably simple universal behavior. Deviations from this underlying behavior can be expected to lead to new insight into the nonuniversal features exhibited by certain compounds.

Conventional and Unconventional Metal–Organic Frameworks Based on Phosphonate Ligands: MOFs and UMOFs

Conventional and Unconventional Metal–Organic Frameworks Based on Phosphonate Ligands: MOFs and UMOFs

Mutagenesis of Beryllium-Specific TCRs Suggests an Unusual Binding Topology for Antigen Recognition

Unconventional Ags, such as metals, stimulate T cells in a very specific manner. To delineate the binding landscape for metal-specific T cell recognition, alanine screens were performed on a set of Be-specific TCRs derived from the lung of a chronic beryllium disease patient. These TCRs are HLA-DP2-restricted and express nearly identical TCR Vβ5.1 chains coupled with different TCR α-chains. Site-specific mutagenesis of all amino acids comprising the CDRs of the TCRA and TCRB genes showed a dominant role for Vβ5.1 residues in Be recognition, with little contribution from the TCR α-chain. Solvent-exposed residues along the α-helices of the HLA-DP2 α- and β-chains were also mutated to alanine. Two β-chain residues, located near the proposed Be binding site of HLA-DP2, played a dominant role in T cell recognition with no contribution from the HLA-DP2 α-chain. These findings suggest that Be-specific T cells recognize Ag using an unconventional binding topology, with the majority of interactions contributed by TCR Vβ5.1 residues and the HLA-DP2 β1-chain. Thus, unusual docking topologies are not exclusively used by autoreactive T cells, but also for the recognition of unconventional metal Ags, such as Be.

Employment of Finite Element Modelling and Design of Experiments to Investigate the Geometrical Factors in T-Type Bi-Layered Tube Hydroforming

In the last years many researchers were concentrating to develop and design new unconventional metal forming processes. Among such new technologies, tube hydroforming was proved as one of the most promising. Geometry of the tube and die were found to have significant effects on the hydroformed part. In this work, Response surface method was used based on data provided by Finite element modeling to construct a model for the bulge height as a function of geometrical factors for T-type bi-layered tube hydroforming. Interaction effects were analyzed and discussed.

Unchanged thermopower enhancement at the semiconductor-metal transition in correlated FeSb2−xTex

Substitution of Sb in FeSb2 by less than 0.5% of Te induces a transition from a correlated semiconductor to an unconventional metal with large effective charge carrier mass m∗. Spanning the entire range of the semiconductor-metal crossover, we observed an almost constant enhancement of the measured thermopower compared to that estimated by the classical theory of electron diffusion. Using the latter for a quantitative description one has to employ an enhancement factor of 10–30. Our observations point to the importance of electron-electron correlations in the thermal transport of FeSb2, and suggest a route to design thermoelectric materials for cryogenic applications.

Integration of finite element analysis and design of experiments to analyse the geometrical factors in bi-layered tube hydroforming

Tube hydroforming (THF) is a type of unconventional metal forming process in which high fluid pressure and axial feed are used to deform a tube blank in the desired shape. Bi-layered tube hydroforming is suitable to produce bi-layered joints to be used in special applications such as aerospace, oil production and nuclear power plants. In this work, a finite element study along with response surface methodology (RSM) for design of experiment (DOE) has been used to construct models for three responses namely: bulge height, thickness reduction, and wrinkle height as a function of geometrical factors for X shape bi-layered tube hydroforming. A finite element model was built and experimentally validated. The models developed using finite element analysis (FEA) and RSM was found to be educated. The factors effect and their interactions on the three responses were determined and discussed. Such integration was proved to be a successful technique that can be used to predict the geometry of the hydroformed part.

Noble metals in graphitized rocks of the Khanka terrain (Primorye): Evidence from analytical results based on decomposition by the fluoroxidizing method

Development of the geology, geochemistry, and analytical chemistry of noble metals (NM) in the past 30 years has provided new insights into the nature of unconventional complex gold and platinum group metal (PGM) deposits. In particular, such deposits confined to black shales were discovered in Caledonides of the Central Asian orogenic belt, such as the well-known Muruntau, Kumtor, Zun-Kholba, Irokinda, Sukhoi Log, Nezhdaninskoe, Natalka, and others. In the past 10‐15 years, commercial PGM concentrations were detected in ores of these deposits [1‐4 and others]. The PGMs in these deposits are traditionally assigned to the carbonaceous matter (CM) of rocks. However, it turned out that they are likely (and primarily) associated with sulfides. Geochemical aspects of PGM concentration in rocks (and ores) and issues of their reliable determination have attracted the main attention in discussions devoted to the problem of PGM occurrence in black shales in the recent period of more than 20 years [4, 5, and others]. The Khankai massif is located at the center of the Central Asian orogenic belt in the Russian Far East. The NM mineralization (Au + PGM) was recently discovered in graphitized rocks [6] of the well-known graphite deposits in the Lesozavodsk region of Primorye [7]. Relative to the typical black shales mentioned above, these rocks are almost devoid of sulfides [8]. However, this interesting feature is provoked apparently by technical difficulties in the analysis of PGMs. For example, analysis of Au and Pt by glow discharge ion mass spectrometry (GDI MS) [9] yielded 3‐30 and 4‐52 g/t, respectively. Duplicate analysis of the same samples by atomic coupled plasma atomic emission spectrometry (ICP AES) and atomic absorption spectrometry by thermoelectric atomization with prior extract concentration (EC TEA) yielded, on average, two orders of lower Au concentrations, while the presence of Pt was not confirmed at all [10]. However, such contradictory results are common for the analysis of black shales due to both poor representativeness of the samples analyzed and losses of the NM during the chemical preparation of samples and their transfer to solutions, as was demonstrated for the Natalka deposit [5, 11, and others].