Anomalous Metal Research Articles

Variational Monte Carlo Study of Electron Differentiation around Mott Transition

We study ground-state properties of the two-dimensional Hubbard model at half filling by improving variational Monte Carlo method and by implementing quantum-number projection and multi-variable optimization. The improved variational wave function enables a highly accurate description of the Mott transition and strong fluctuations in metals. We clarify how anomalous metals appear near the first-order Mott transition. The double occupancy stays nearly constant as a function of the on-site Coulomb interaction in the metallic phase near the Mott transition in agreement with the previous unbiased results. This unconventional metal at half filling is stabilized by a formation of “electron-like pockets” coexisting with an arc structure, which leads to a prominent differentiation of electrons in momentum space. An abrupt collapse of the “pocket” and “arc” drives the first-order Mott transition.

Spin fluctuations and the "strange metal" behavior of a weakly doped antiferromagnet

We analyze the spectral properties of a phenomenological model for a weakly doped two-dimensional antiferromagnet, in which the carriers move within one of the two sublattices where they were introduced. Such a constraint results in the free carrier spectra with the maxima at ${\bf k}=(\pm \pi /2 ,\pm \pi /2)$ observed in some cuprates. We consider the spectral properties of the model by taking into account fluctuations of the spins in the antiferromagnetic background. We show that such fluctuations lead to a non-pole-like structure of the single-hole Green's function and these fluctuations can be responsible for some anomalous strange metal properties of underdoped cuprates in the nonsuperconducting regime.

高温超伝導体の異常金属相における輸送現象の理論 : フェルミ液体論に基づく統一的理解(最近の研究から)

高温超伝導体の異常金属相における輸送現象の理論 : フェルミ液体論に基づく統一的理解(最近の研究から)

Geology and Chemistry of the El Abuelo Calcic Fe-skarn and Related Cu-(Ag)-Bearing Hydrothermal Veins, Chubut Province, Southern Argentina

The El Abuelo Ca-Fe-magnetite skarn and related hydrothermal quartz veins are located at Cerro Pepita Hill, in southwestern Chubut province of southern Argentina, 1700 km southwest of Buenos Aires. These deposits are developed in a continental magmatic arc environment linked to the Andean orogeny. Iron skarn mineralization is mainly hosted by an Upper Jurassic to Early Cretaceous sedimentary sequence interbedded with Upper Jurassic basaltic andesite, and is spatially associated with Early Cretaceous calc-alkaline dikes. Ore grades vary between 40 and 63 wt.% Fe. In addition, anomalous metal contents (>10 000 ppm Cu and up to 81 g/t Ag) are present in the hydrothermal quartz veins. At least three paragenetic mineral assemblages have been identified in the El Abuelo exoskarn: (1) amphibole > epidote ± chlorite ± quartz, formed by isochemical contact metamorphism; (2) Fe-clinopyroxene ± Ca-garnet, formed during prograde metasomatic anhydrous exoskarn formation; and (3) actinolite ± epidote ± chlorite ± quartz ± magnetite > titanite, resulting from hydrous retrograde alteration of exoskarn. Endoskarn alteration involved an early Mg-Fe-clinopyroxene ± Fe-garnet assemblage followed by retrograde actinolite replacement of pyroxene. Lower temperature hydrothermal alteration related to quartz veins was superimposed on the skarn assemblages, showing an innermost sericite ± adularia ± pyrite ± chalcopyrite assemblage and an external propylitic halo. Some metallogenic characteristics of the mineralization and the geological setting resemble those in several iron oxide copper-gold deposits elsewhere in the world.

Dimensionality of the electronic states in [formula omitted] studied by soft X-ray photoemission

The electronic states of Nd 0.45 Sr 0.55 MnO 3 in the two-dimensional metal phase have been revealed by the high-resolution Mn 2 p – 3 d resonant photoemission. The vanishingly weak intensity at E F indicates an anomalous metal due to the two-dimensionality of the electronic states.

Correlation between Diffusion Parameters and the Temperature-Dependent Modulus of Elasticity of Metals

It is shown using the Debye model and an equation of state for solids that the diffusion parameters of anomalous and conventional metals correlate with the temperature variation of their shear moduli.

Relaxor ferroelectric behavior and collective modes in theπ−dcorrelated anomalous metalλ−(BEDT−TSF)2FeCl4

We have investigated the microwave response at 44.5 GHz with respect to temperature T and external magnetic field H in $\ensuremath{\lambda}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TSF}{)}_{2}{\mathrm{FeCl}}_{4}$ forming a quasi two-dimensional electronic system with $\ensuremath{\pi}\ensuremath{-}d$ correlations. At 8.3 K $[{=T}_{\mathrm{MI}},$ the metal-insulator (MI) transition temperature] $<T<70\mathrm{K}$ ${(=T}_{\mathrm{FM}}),$ the microwave dielectric constant along the c axis, ${\ensuremath{\epsilon}}_{1}^{c},$ takes positive large values amounting to 1000--2000. Furthermore, the microwave conductivity ${\ensuremath{\sigma}}_{1}^{c}$ starts to deviate resistively from the dc conductivity ${\ensuremath{\sigma}}_{\mathrm{dc}}^{c},$ and the difference between ${\ensuremath{\sigma}}_{1}^{c}$ and ${\ensuremath{\sigma}}_{\mathrm{dc}}^{c}$ reaches about two orders of magnitude just above ${T}_{\mathrm{MI}}.$ The present results are consistent with the previous results at 16.3 GHz, and consequently the appearance of the anomalous metallic state is confirmed. An anomalous microwave response has also been observed in the ${a}^{*}$ and ${b}^{*}$ directions, and there exist large anisotropies depending sensitively on the orientations. The broad maximum of ${\ensuremath{\epsilon}}_{1}^{c}$ around 30 K is reminiscent not of a usual ferroelectric transition, but of relaxor ferroelectric behaviors. It is expected that dielectric domains or stripes with less metallic conductions emerge inhomogeneously in the $\ensuremath{\pi}$ electronic systems. Above ${T}_{\mathrm{FM}},$ where microwave anomalies are not present, the interplane and intraplane microwave conductivities hold anisotropies ${\ensuremath{\sigma}}_{1}^{c}/{\ensuremath{\sigma}}_{1}^{{b}^{*}}\ensuremath{\approx}{10}^{3}$ and ${\ensuremath{\sigma}}_{1}^{c}/{\ensuremath{\sigma}}_{1}^{{a}^{*}}\ensuremath{\approx}10.$ In the antiferromagnetic insulating state, ${\ensuremath{\sigma}}_{1}^{c}$ becomes much conductive in comparison with ${\ensuremath{\sigma}}_{\mathrm{dc}}^{c}.$ Together with low frequency data, ${\ensuremath{\epsilon}}_{1}^{c}$ is found to exhibit a large frequency dispersion. The microwave response is not attributed to single particle excitations, but to some collective mode excitations associated with charge degrees of freedom. The $H\ensuremath{-}T$ phase diagram of the MI transition determined by the present microwave measurements is independent of the orientations of H, and coincides well with the phase diagram obtained by the dc magnetoresistivity and magnetization. Spin waves for the hard axis are observed as an absorption peak in the width change for the microwave magnetic field applied parallel to both H and ${a}^{*}.$

Geology and Metallogenic Evolution of the PolymetallicDeposits of the Alcudia Valley Mineral Field, Eastern Sierra Morena, Spain

The Alcudia Valley is intensely mineralized, with a large number of Pb-Zn-Ag-Cu deposits hosted by Neoproterozoic and Paleozoic sedimentary rocks. Five distinct types of deposits have been recognized. The most significant mineralizing events were related to the two major phases of deformation (HD1, HD2) and granite emplacement during the Hercynian orogeny. Stable isotope and lithogeochemical data demonstrate that the metals, as well as sulfur and carbon, were sourced from the local sedimentary rocks. Type A deposits are minor occurrences of strata-bound mineralization with Zn > Pb, occurring as disseminations and small veins in Late Ordovician limestone. A syndiagenetic origin is suggested by the limited stratigraphic distribution of the mineralization and anomalous base metal contents of Late Ordovician-Early Silurian black shales overlying the mineralized limestone. Minor remobilization of disseminated sulfides into joints took place during late diagenesis or early Hercynian deformation. Types B, C, and D are syntectonic deposits with Zn > Pb. Type B deposits are strongly deformed veins in HD1 fractures in Ordovician rocks. A process involving local mobilization of metals by a surface-derived fluid is indicated by depleted metal contents of host rocks adjacent to the veins, the similarity of δ 34S values of ore sulfides with disseminated pyrite in the host rocks, and the δ 18OH2O values. Type C deposits exhibit a greater variation in morphology and degree of deformation compared to other types and are found in both HD1 and HD2 fractures in Late Ordovician and Silurian rocks. The stratigraphic distribution and δ 34S values of sulfides are similar to type A deposits, suggesting that localized hydrothermal systems either remobilized type A mineralization or derived metals and sulfur from the same source. Type D deposits occur in HD2 shear fractures in Neoproterozoic rocks. The δ 13C values of carbonate gangue and the similarity of δ 34S values of ore sulfides and disseminated pyrite in the host rocks indicate that black shales of the Neoproterozoic sequence are the major source of sulfur and carbon. Mixing of a metamorphic fluid with a surface-derived fluid is suggested by fluid inclusion and oxygen isotope data. Type E deposits, the most abundant and economically most important type, are post-tectonic Pb > Zn veins occupying HD2 fractures and are widely distributed through the district in rocks ranging from Neoproterozoic to Late Ordovician. Mineral assemblages and Ag contents of the veins show a zonal relationship with respect to monzogranite outcrops, indicating that late Hercynian magmatism was the source of heat driving fluid migration through the fracture system. Fluid inclusion and oxygen isotope data are typical of basinal brines. Reaction of the fluid with black shales of the Neoproterozoic sequence is suggested by δ 34S values of sulfides and δ 13C values of carbonates of the main stages of the paragenetic sequence. The final paragenetic stage consists of barite, calcite, and pyrite, which may have been deposited during a later hydrothermal event, probably in the Early Triassic.

Haemorrhagic diarrhoea and reproductive failure in Bonsmara cattle resulting from anomalous heavy metal concentrations in soils, forages and drinking water associated with geochemical anomalies of toxic elements on the farm Puntlyf, South Africa

Poor livestock health conditions are associated with geochemical Pb anomalies on a farm approximately 40 km east of Pretoria, South Africa. A generic risk assessment of drinking water for Bonsmara cattle obtained from three separate subterranean water sources on the farm, revealed the presence of several potentially hazardous constituents suspected for the development of adverse health effects in the herd. The two main symptoms of the herd, namely, severe haemorrhagic diarrhoea in calves and reproductive failure in cows, have been investigated. A selenium-induced copper deficiency was proposed as the main cause to the calf diarrhoea, due to complexing between high concentrations of Se, Mo, Hg and Pb in drinking water. It was also anticipated that such Cu deficiencies would lead to low systemic Se inducing hypothyroidism in the cows due to inadequate iodine activation required for thyroid hormone formation and consequently adversely affect reproduction. The anomalous Pb in borehole drinking water on the southern part of the farm, suggests a clear genetic link with the underlying geochemical Pb anomalies detected by means of an ongoing regional geochemical survey.

Trace metal occurrence and distribution in sediments and mangroves, Pumicestone region, southeast Queensland, Australia

The Pumicestone region is a unique catchment in northern Moreton Bay, southeast Queensland. The region supports a wide range of land-use activities as well as attractions such as nature conservation areas. One environmental aspect that has not previously been addressed in this area is the occurrence of minor and trace metals in estuarine sediments associated with the main estuaries of the region. The trace metals included in this investigation are: vanadium, chromium, molybdenum, cobalt, nickel, copper, zinc, cadmium, lead and arsenic. To determine and evaluate the occurrence and distribution of metals in the area, several components have been analysed: bedrock material, pre-industrial settings, recent estuarine sediments, soils of estuarine origin and mangrove pneumatophores. The 40 sites chosen for sediment and soil samples cover a variety of estuarine settings and represent a range of natural conditions in terms of channel and bank morphology, tidal energy, vegetation cover, relationship to bedrock, water salinity and land disturbance. The chemical, mineralogical and statistical analyses employed in this study enabled (a) establishment of background values for the area, (b) determination of relationships between metals and (c) identification of sites with anomalous metal concentrations. All the metals found in the sediments of the area are sourced from the geological bedrock. The dominant trace elements identified in sediments are Zn, V and Cr. The remaining metals are highly variable spatially. All trace metals are controlled by the presence of Fe and Mn oxides, and by the grainsize of the sediment. Typically, fine-grained Fe-rich materials tend to adsorb more trace metals than sandy sediments. In soils that have developed from estuarine muds, some metals such as Cr, Mo, Pb and As tend to be in larger quantities than in the estuarine counterparts. Some of the elements, which occur in significant amounts in the sediment, have been detected in mangrove tissue ( Avicennia marina) such as V, Cr, Zn, Fe and Mn. Of particular note is Cu, which is present in mangrove tissue in quantities many times exceeding the sediment concentration. The comparative analysis of pre-industrial settings and recent sediments and soils highlighted some areas of metal enrichment such as acid-affected sites where oxidation of pyrite has mobilised metals from sediments; these metals are then redistributed in Fe-rich surficial layers. Disturbed banks within the estuaries are also likely to have low levels of metal enrichment due to boating activities.

HIGH-RESOLUTION ANGLE-RESOLVED PHOTOEMISSION STUDY OF BaCo1-xNixS2

We have performed angle-resolved photoemission spectroscopy on a layered Mott system BaCo 1-x Ni x S 2 across the phase transition from the antiferromagnetic insulator (x = 0.18) to anomalous metal (x = 0.28). In the anomalous metallic phase, we found a large Fermi surface centered at the M(A) point with a dominant Co (Ni) 3d3z2-r2 character. Hubbard bands in the insulating phase have a remnant of Fermi surface in the metallic phase and gradually evolve into metallic dispersive bands upon carrier doping. We conclude that the electronic structure of BaCo 1 - x Ni x S 2 is basically different from that of the high-Tc cuprates although the transport and magnetic properties share some common features between the two layered compounds.

Evolution of metallic states from the Hubbard band in the two-dimensional Mott systemBaCo1−xNixS2

We report angle-resolved photoemission spectroscopy on the layered Mott system ${\mathrm{BaCo}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{S}}_{2}.$ $(x=0.18,$ 0.28) across the phase transition from the antiferromagnetic insulator to anomalous metal. We found that the lower Hubbard band in the insulating phase possesses a remnant of the Fermi surface in the metallic phase and gradually evolves into the metallic bands with carrier doping. We compare the experimental result with those of the high-${T}_{c}$ cuprates to discuss the absence of superconductivity in ${\mathrm{BaCo}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{S}}_{2}.$

The Enhancement of Diffusion Processes in BCC Phases of Anomalous Metals by Fluctuation-Induced Frenkel Pairs

The Enhancement of Diffusion Processes in BCC Phases of Anomalous Metals by Fluctuation-Induced Frenkel Pairs

Anomalous metallicity and electronic phase separation in theCsC60polymerized fulleride

133Cs and 13C-NMR have been used to study the electronic properties of the polymerized phase of CsC60 at ambient and under hydrostatic pressure. The salient result of this study is the finding of fluctuations in the local field at 133Cs site which are independent of the applied pressure and due to thermally activated changes in the local electronic environment of 133Cs nuclei. We establish that the phase separation between magnetic and nonmagnetic domains observed in the low temperature state at ambient pressure is the result of a slowing down of these fluctuations likely related to polaronic charge excitations on the polymers.

Pseudogap induced by superconducting fluctuation and anomalous metals in high- Tc superconducting materials

The pseudogap in the single particle spectrum induced by the superconducting fluctuation together with the antiferromagnetic spin fluctuation has been believed to play key roles to determine essential features of anomalous properties of Cu-oxide high- T c superconducting materials observed at temperatures higher than the superconducting transition temperature T c. The roles are described as follows: in metals near Mott insulators, doped holes create new states inside the charge transfer gap called as ingap states, which have band width proportional to the hole doping rate δ and interact with each other through the superexchange interaction J s enhanced by the antiferromagnetic spin fluctuation. This effective interaction promotes superconducting fluctuation, which induces a pseudogap in the single particle spectra. On the other hand, the pseudogap suppresses the spin fluctuation. Thus, effects of both of the spin fluctuation and the superconducting fluctuation need to be treated in a consistent way. In an underdoped system, the spin fluctuation dominates at higher temperatures, while the superconducting fluctuation or the pseudogap effect dominates at lower temperatures above T c. This competition determines the anomalous temperature dependence of systems. We demonstrate the senario explicitly by taking the d–p model with the help of the 1/ N-expansion theory and calculating T c, the NMR relaxation rate 1/ T 1 and the single-particle spectrum.

Determining the cutoff between background and relative base metal smelter contamination levels using multifractal methods

For a specified, spatially distributed geoscience variable measure, log–log plots of contour interval versus cumulative contour area for all contours exceeding a specified contour value can provide insight into the nature of the multifractal spectrum; e.g. if there are sharp bends or breaks. These can be estimated graphically by plotting lines of best fit and finding their solution on a log–log graph of contour interval versus cumulative area per contour interval. The breakpoint between background and anomalous values is defined when the spectrum is relatively close to its minimum value. A new computer program using M ap I nfo 4.1, V ertical M apper 1.5 and E xcel 5.0 has been developed for the preceding method. As an example of application, variation in estimated background metal concentration cutoffs is illustrated using humus geochemistry in the vicinity of a base metal smelter near Flin Flon, Manitoba. Cutoffs between background and anomalous metal concentrations of copper, zinc and mercury are estimated using the multifractal area-concentration model. These metals return to background geochemical levels within approximately 142, 104 and 105 km from the source respectively.

Correlation between the Limiting pH of Metal Ion Solubility and Total Metal Concentration

As an alternative to species distribution diagrams (pM vs pH curves in aqueous solution) drawn for a fixed total metal concentration, this work has developed simple linear models for correlating the limiting pH of metal ion solubility—in equilibrium with the least soluble amorphous metal hydroxide solid phase—to the total metal concentration. Thus adsorptive metal removal processes in complex systems can be better designed once the limiting pH of heavy metal solubility (i.e., pH*) in such a complex environment can be envisaged by simple linear equations. pH* vs pMt (Mt = total metal concentration that can exist in aqueous solution in equilibrium with M(OH)2(s)) linear curves for uranyl–hydroxide, uranyl–carbonate–hydroxide, and mercuric–chloride–hydroxide simple and mixed-ligand systems and cupric–carbonate–hydroxide complexes in equilibrium with mixed hydroxide solid phases may enable the experimental chemist to distinguish true adsorption (e.g., onto hydrous oxide sorbents) from bulk precipitation removal of the metal and to interpret some anomalous metal fixation data—usually attributed to pure adsorption in the literature—with precipitation if the pMt at the studied pH is lower than that tolerated by pH* vs pMt curves. This easily predictable pH* corresponding to a given pMt may aid the design of desorptive mobilization experiments for certain metals as well as their adsorptive removal with the purpose of simulating metal adsorption and desorption cycles in real complex environments with changing groundwater pH.

Zn, Pb, Cu and As distribution patterns in overbank and medium-order stream sediment samples: their use in exploration and environmental geochemistry

Overbank and medium-order stream sediment samples were collected in Belgium and Luxembourg from 66 sampling locations (area of about 33,000 km 2) and analysed for major and trace elements among which Zn, Pb, Cu and As. At each sampling location large bulk samples were taken, namely in the lower (normally at ≥1.5 m depth, over an interval of about 20–40 cm) and upper (normally upper 5–25 cm) parts of the overbank profiles and from the stream sediments. Furthermore, at a number of these sites, a detailed geochemical analysis of vertical overbank sediment profiles (sampling intervals of 10–20 cm) was subsequently carried out to unravel element variations through time and to help in the overall evaluation. For most sampled sections evidences such as 14C-dating and the absence of anthropogenic particles point towards a pre-industrial and often pristine origin of the lower overbank sediment samples. From the latter bulk samples, mean background concentrations were deduced. They reveal the existence of significant differences between the northern and southern part of Belgium (incl. Luxembourg) which relate to the difference in geological substrate. In the north dominantly non-lithified Quaternary and Tertiary sands, marls and clays occur while in the south Palaeozoic sandstones, shales and carbonate rocks outcrop. Consequently separate mean background values were calculated for the two areas. In the southern study area, some anomalous metal concentrations have been recorded in pre-industrial sediments. They are derived from mineralised Palaeozoic rocks, a feature which could be of interest for base metal exploration. In the upper overbank and stream sediments, in general, higher heavy metal and As contents were recorded with highest values in areas with metal mining, metal melting and cokes treatment industries. By comparing the trace element concentrations of the upper overbank or stream sediment samples with the concentrations detected in the lower overbank samples at each of the sampling locations, and by evaluating the vertical distribution patterns where available, the degree of pollution of the alluvial plain and the present-day stream sediments can be assessed. From this exercise, it is clear that highest pollution occurs in the northern part of Belgium, which relates to its high population density and industrial development.

Metal-insulator transitions

Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and $t\ensuremath{-}J$ models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in $d$-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and orbital fluctuations, mass renormalization effects, incoherence of charge dynamics, and phase transitions under control of key parameters such as band filling, bandwidth, and dimensionality. These parameters are experimentally varied by doping, pressure, chemical composition, and magnetic fields. Much of the observed behavior can be described by the current theory. Open questions and future problems are also extracted from comparison between experimental results and theoretical achievements.

A study of the analytical parameters important for the sequential extraction procedure using microwave heating for Pb, Zn and Cu in calcareous soils

A four-step microwave extraction procedure, using microwave heating, for Pb, Zn and Cu fractionation has been elaborated for calcareous soils. This procedure distinguishes the metal fraction bound to carbonate, to iron and manganese oxides, to organic matter and the residual fraction. Sample and analytical variances have been estimated to identify the anomalous metal contents in the light of the variation in the concentration among the samples. Performances of each step of the method have also been calculated. The validity of the method was verified by a mass balance using calcareous soils and two certified reference materials. The results obtained were appropriate for the assessment of the environmental risks.