Unusual Electronic States Research Articles

Unusual Electronic State of the Low-Carrier System CeSb under High Pressure Studied by Simultaneous Measurement of Electrical Resistivity and Lattice Parameter

We have studied the origin of the anomalous peak structure of resistivity of the low-carrier system CeSb appeared around the antiferromagnetic transition temperature T N under high pressures by means of simultaneous measurement of lattice parameter by X-ray diffraction and resistivity together with neutron diffraction technique. It was found that there is a strong relationship between the unusual decrease of lattice parameter and the unusual increase of resistance below T N under high pressure. Both of these phenomena can be explained by the appearance of Γ 8 -like magnetic state of Ce 3+ ion below T N .

Unusual Electronic State of Layered θ-(ET)2 X Studied by Raman Spectroscopy

Employing Raman spectroscopy, we have studied the electronic structure of the charge-ordering system, θ-(ET)2X, the dihedral angle (ϕ) of which ranges from 100° to 121°. The most stable metal, θ-(ET)2I3, (ϕ=100°) has a uniform charge distribution in a whole temperature range. The compounds with ϕ>111° have an inhomogeneous charge distribution even above the CO transition, which implies that the charges have localized nature in a whole temperature range. These localized charges are long-range ordered in the CO phase, whereas they are fluctuating randomly or forming short-range ordered domains above the CO phase transition.

Unusual electronic state of layered θ-(ET)2X studied by raman spectroscopy

Unusual electronic state of layered θ-(ET)2X studied by raman spectroscopy

Ｓｒ２ＦｅＭｏＯ６エピタキシャル薄膜の表面特性

Thin films of ordered double perovskite Sr2FeMoO6 were sputter-deposited on Ba0.4Sr0.6TiO3-buffered SrTiO3 substrates, and their surface properties were examined by atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS). The Mo 3d spectra of Sr2FeMoO6 films showed a multiple peak structure, which originated from the unusual electronic state of metallic Sr2FeMoO6. Systematic XPS studies of the air-exposed surface of Sr2FeMoO6 film indicated that the surface native barrier was an insulating SrMoO4. In addition, a TMR junction with the native barrier was fabricated using a convention photolithographic technique, and an MR ratio of 10 % was observed at 4.2 K.

High-resolution photoemission spectroscopy of d,f electron systems at the Hiroshima Synchrotron Radiation Center

Recently, high energy-resolution and low-temperature photoemission spectroscopies (Δ E=4.5∼20 meV and T=6∼300 K) have been realized successfully on undulator beamlines installed at the compact light source at the Hiroshima Synchrotron Radiation Center. In the case of Kondo semimetal CeNiSn, the temperature dependence of the spectra provides clear evidence of pseudogap formation below the characteristic temperature between 50 and 60 K. Resonant photoemission spectra of the Kondo semiconductor CeRhAs and the Kondo semimetal CeRhSb revealed unusual Ce 4f-derived electronic states. The spectral features of CeRhAs differ considerably from the predictions of a periodic Anderson model, while the features of CeRhSb are well described by the model. The spectra of Y 1− x Ca x TiO 3 ( x=0.39) exhibits a sharp Fermi edge at low temperature, corresponding to the metal–insulator transition at ∼150 K, where the carrier density in the Ti 3d bands plays an important role.

Unconventional magnetic transition and transport behavior inNa0.75CoO2

Here we report an unconventional magnetic and transport phenomenon in a layered cobalt oxide, NaxCoO2. Only for x = 0.75, a magnetic transition of the second order was clearly detected at Tm ~ 22 K where an apparent specific-heat jump, an onset of extremely small spontaneous magnetization, and a kink in resistivity came in. Moreover large positive magnetoresistance effect was observed below Tm. These features of the transition strongly indicate the appearance of an unusual electronic state that may be attributed to the strongly-correlated electrons in Na0.75CoO2.

Kristallstrukturen und elektronische Eigenschaften von Ge1/3NbS2 und Ge1/4NbS2 / Crystal Structures and Electronic Properties of Ge1/3NbS2 and Ge1/4NbS2

Single crystals of the intercalation compounds Ge1/3NbS2 andGe1/4NbS2 have been prepared by heating of the elements at 1073 K and by chemical transport with iodine at 923 to 1073 K. Their crystal structures were determined by single crystal X-ray methods.Ge1/3NbS2 (P63/mcm, a=5.767(1), c=13.518(3) Å, Z = 6) crystallizes with a superstructureof 2H-NbS2, characterized by layers of edge-sharing NbS6 trigonal prisms. The Ge atoms in the octahedral voids of the van der Waals gap are sixfold coordinated by sulfur. The NbS2-sublattice of Ge1/4NbS2 (P63/mmc, a = 3.339(1), c = 37.326(7) Å , Z = 6) represents a new 6H-polymorph. Herein, the Ge atoms are located either in the centers of the octahedral voids (c. n. = 6) or shifted from this position along [001] (c. n. = 3 + 3). The unusual electronic state and the bonding situation of germanium in the van der Waal gaps of NbS2 and the metal-metal bonding are studied in detail by using DFT band structure calculations.

Electronic structure of atomic chains on vicinal Si(111)-Au

Unusual electronic states are found for gold-induced chain and ladder structures on vicinal Si(111) surfaces, such as $\mathrm{Si}(111)5\ifmmode\times\else\texttimes\fi{}2\ensuremath{-}\mathrm{Au}$ and Si(557)-Au. As two-dimensional reference the $\mathrm{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}\mathrm{Au}$ surface is investigated. The highly stepped Si(557)-Au surface is metallic, despite an even electron count. That is explained by two half-filled, nearly degenerate bands. On the $\mathrm{Si}(111)5\ifmmode\times\else\texttimes\fi{}2\ensuremath{-}\mathrm{Au}$ surface we find a band that changes continuously from one dimensional at its maximum to two dimensional at its minimum. It exhibits a pseudogap within 0.3 eV of the Fermi level ${E}_{F},$ where the spectral weight is strongly reduced. $\mathrm{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}\mathrm{Au}$ exhibits an electron pocket at $\ensuremath{\Gamma}$ that changes its filling continuously with increasing Au coverage.

Fermi surface, pseudogap and superconducting gap in La 2− xSr xCuO 4

The electronic structure of La 2− x Sr x CuO 4 (LSCO) has been revealed by a series of photoemission spectroscopic studies. The unusual electronic states in the underdoped regime are attributed to the large and small pseudogap formation, which has been observed in other high- T C cuprates, and stripe fluctuations, which are particularly pronounced in LSCO.

NMR study of Sc 1− xU xPd 3 under non-fermi liquid state

We have performed 45Sc NMR measurements on the Sc 1− x U x Pd 3 system, which exhibits an unconventional Kondo effect with a non-Fermi liquid character at low temperatures for the samples with x⩽0.3. The relaxation rates, 1/ T 1, for the x=0.3 and 0.25 samples are strongly enhanced by magnetic fluctuations below 30 K in low magnetic field, where other macroscopic properties show typical NFL behavior. Since the x=0.2 samples show Korringa ( T 1 T=const.) behavior, this enhancement in the x=0.3 and 0.25 samples may be associated with an unusual electronic state near the quantum critical point. Below 1 K , T 1 in the x=0.3 sample seems to obey a 1/ T 1∝ T relation. This behavior may be associated with the enhanced Korringa relation in the vicinity of the quantum critical point.

Metal-insulator transition in a degenerate Hubbard model

We have studied the metal-insulator transition at integer fillings in a triply degenerate Hubbard model using the Lanczos method. The critical Coulomb interaction strength U-c, is found to depend strongly on the band filling, with U-c similar to root 3 W (W is the bandwidth) at half filling for this case with threefold degeneracy. We discuss the implications of our results on metal-insulator transitions in strongly correlated systems in general, and on the unusual electronic ground state of the alkali-metal-doped fullerenes, in particular. [S0163-1829(99)11003-8].

Theory of high-temperature superconductivity in underdoped cuprates; the unusual electronic structure and the origin of the pseudogap

By reviewing the first-principles studies of the many-electron electronic structures of underdoped and performed by Kamimura and co-workers, unusual electronic states are clarified. That is, the dopant holes move coherently by taking the Zhang-Rice spin singlet and Hund's coupling spin triplet alternately in the spin-correlated region of antiferromagnetic ordering due to the Cu localized spins, without destroying the antiferromagnetic order. This creates a metallic state which leads to superconductivity. The coexistence of (i) the antiferromagnetic spin ordering and (ii) the ordering in the appearance of the Zhang-Rice singlet and the Hund's coupling triplet results in the small Fermi surface for a carrier system and also leads to the decrease in the electronic entropy below a certain temperature at which the Fermi surface changes from a larger one to smaller ones. This is the microscopic origin of the pseudogap, the concept of which was originally proposed by Loram and co-workers in terms of the Fermi liquid picture.

Mossbauer resonance: A well adapted characterization method of unusual electronic configurations or oxidation states of iron stabilized under high oxygen pressure conditions

Abstract During these last twenty years high oxygen pressure techniques have led to the stabilization of unusual electronic configurations or oxidation states of d-elements. Due to the specific equipment the quantity of material elaborated in high pressure-high temperature conditions are small(100-500 mg).In such a case a non-destructive characterization is important. For iron oxides, Mö ssbauer resonance has allowed to point out the stabilization of the high spin state for Fe(IV) in the (A, A')2M'0,50Fe05,0O4 oxides(A =Ca, Sr, Ba; A' = La; M'=Li, Mg, Zn prepared under oxygen gas pressure (0, 05 < P < 0, 4 GPa). Another illustration is the characterization, for the first time, of six-coordinated Fe(V) in the ordered perovskite La Li2FeO6elaborated in a belt apparatus (7GPa, 900° C) using the "in situ" decomposition of KClO3 as oxygen source.

Anisotropic properties of high-T c single crystals disordered by fast neutron irradiation

Anisotropy of electrical resistivity, Hall effect and the upper critical field in high-T c YBCO and NdCCO single crystals depending on disorder caused by fast neutron irradiation is investigated. To find out the features typical for HTSC's themselves we studied the same physical properties of other anisotropic single crystals. Though all the systems under study have some physical properties in common, the response of HTSC's to disorder evidences for unusual electronic states of these compounds.

Is the high-T c superconductivity associated with unusual electronic states of the elements?

The general crystallochemical and electronic features of high-Tc materials are considered. It is claimed that in complex high-Tc oxides there takes place charge transfer from oxygens in the BaO or SrO sheets to the neighbouring structural fragments formed by metals of fluctuating valence (Cu, Bi, Tl, Pb). In these cases the more stable structures are those in which atoms with fluctuating valence are present in lower valence states. A conclusion is made that appearance of high Tc superconductivity is due of unusual valence states of oxygen (O −type) and metal atoms (Bi 2+, Tl 2+ type) or perhaps of bound states of (M + + M 3+) type with fast electronic exchange between the atoms.

Unusual electronic state for iron in the superconductor

Unusual electronic state for iron in the superconductor

Isolated atoms, molecules and clusters

The basic constituents of matter, namely, atoms molecules and small clusters can be isolated in a solid rare-gas-matrix (RGM) and be characterized by Mossbauer Spectroscopy (MS). Experiments can be conducted both by the absorption method using a co-evaporation method of Mossbauer isotopes or by emission spectroscopy where source nuclei are isolated in the RGM. Experimental aspects of both techniques are outlined. Examples of applications of RGMI-MS are described, namely,57Fe clustering with noble-metals (Cu, Ag, Au); unusual electronic states of Fe following57Co e.c. decay; species formed by the bonding of Fe0, in its ground state, to small molecules are compared with those formed by Fe in its various excited states; and finally, the characterization of atomic I0 and Te0 and Te−1 embedded in a solid argon matrix.

A simple model for predicting the electronic configuration of a dn ion in a tetragonally distorted octahedral environment

A simple, but general model which enables prediction of the electronic structure adopted by ad n ion in an axially distorted octahedron of ligands (D 4h) is described. The variousd n configurations (n = 1 to 9) are briefly reviewed with some recent results concerning the stabilization of unusual electronic configurations or oxidation states in oxides.

Hunting of strange electronic states and structures in solids and biopolymers

It is outlined how the authors arrived at the existence problem of the intermediate states (IS) possibly appearing in bounded crystals with perfect bulk structure and of certain zig-zag states (ZZS) in almost periodic (even disordered) biopolymers. Earlier results are summarized and commented. An example is given for how to enhance the appearance probability of ISS. It is shown that within a narrow critical interval, the width of which is about the eighth of the average separation of the bulk states in the k space of the finite linear chains, any state becomes an his (almost IS), which is very similar to the IS and approaches it continuously. Estimating the effects of in-plane and in-terplane vibrations of stacked aromatic planar compounds on the delocalized π-electron structures, it is concluded that the valence modes have a strong effect on the in-plane π-electronic systems, but a very small one on the interplane π-electronic interactions. The longitudinal acoustical modes of finite polynucleotide DNA models and their root mean square amplitudes are estimated by the method of Peticolas. According to the results obtained, DNA-like and layered graphitelike systems seem to be the probable host systems of 1%. if they exist at all. The appropriateness of the recursion method is discussed to search for unusual electronic states and structures. Such studies are the first unsteady but exciting steps toward the construction of the molecular computers.