http://sces.phys.utk.edu/mostcited/mc1_1114.pdf

Colossal Magnetoresistant Materials: The Key Role of Phase Separation

The study of the manganese oxides, widely known as manganites, that exhibit the ``Colossal'' Magnetoresistance (CMR) effect is among the main areas of research within the area of Strongly Correlated Electrons. After considerable theoretical effort in recent years, mainly guided by computational and mean-field studies of realistic models, considerable progress has been achieved in understanding the curious properties of these compounds. These recent studies suggest that the ground states of manganite models tend to be intrinsically inhomogeneous due to the presence of strong tendencies toward phase separation, typically involving ferromagnetic metallic and antiferromagnetic charge and orbital ordered insulating domains. Calculations of the resistivity versus temperature using mixed states lead to a good agreement with experiments. The mixed-phase tendencies have two origins: (i) electronic phase separation between phases with different densities that lead to nanometer scale coexisting clusters, and (ii) disorder-induced phase separation with percolative characteristics between equal-density phases, driven by disorder near first-order metal-insulator transitions. The coexisting clusters in the latter can be as large as a micrometer in size. It is argued that a large variety of experiments reviewed in detail here contain results compatible with the theoretical predictions. It is concluded that manganites reveal such a wide variety of interesting physical phenomena that their detailed study is quite important for progress in the field of Correlated Electrons.

Colossal-magnetoresistance materials: manganites and conventional ferromagnetic semiconductors

The calculation of the electronic properties of materials is an important task of solid-state theory, albeit particularly difficult if electronic correlations are strong, e.g., in transition metals, their oxides and in f-electron systems. The standard approach to material calculations, the density functional theory in its local density approximation (LDA), incorporates electronic correlations only very rudimentarily and fails if the correlations are strong. Encouraged by the success of dynamical mean field theory (DMFT) in dealing with strongly correlated model Hamiltonians, physicists from the bandstructure and the many-body communities have joined forces and developed a combined LDA + DMFT method recently. Depending on the strength of electronic correlations, this new approach yields a weakly correlated metal as in the LDA, a strongly correlated metal or a Mott insulator. This approach is widely regarded as a breakthrough for electronic structure calculations of strongly correlated materials. We review ...

Electronic structure calculations using dynamical mean field theory

Editor's Preface List of Contributors 1: Wet Chemical Technology 2: Wet Chemical coating Technologies 2.1 Glass Substrates 2.2 Coating Techniques 2.3 Post-Coating Treatment Techniques 2.4 Patterning Techniques 3: Bulk Glass Technologies 4: Coating and Material Properties 4.1 Passive Coatings 4.2 Active Coatings 4.3 Gels, Bulk Materials, Fibers and Powders 4.4 Characterization 5: Subject Index 6: Annex 1. Important Internet Sites 2. Regular Conferences Hosting Sol-Gel Communications 3. Proceedings of Most Important Conferences and Books 4. Where to Find Publications and Reports 5. Market Studies 6. Research Groups and Who's Who in Sol-Gel Science and Technology 7. Companies Commercializing Sol-Gel Related Glass Products and Sol-Gel Products Useful for Glass Production and Organizations which Offer Developments in Sol-Gel Technology 8. Distributors/Manufacturers of Sol-Gel Related Chemical Precursors

Sol-Gel Technologies for Glass Producers and Users

We have found a photoinduced phase transition (PIPT) in the mixed-valence (MV) gold complex ${\mathrm{Cs}}_{2}{\mathrm{Au}}_{2}{\mathrm{Br}}_{6}$ from the MV state (ambient pressure phase) to the single-valence (SV) phase (high-pressure phase) in the pressure region from 6.4 to 6.8 GPa. We have observed an accumulation of the photoirradiation effect of each pulse shot, and have ascribed it to stabilization of the photogenerated SV clusters due to the cooperative Jahn-Teller instability of ${\mathrm{Au}}^{2+}$ ions. The PIPT shows a distinct threshold behavior against the photon density as well as the shots number, which has been interpreted in terms of the critical nucleation of the photoinjected SV clusters. We further found that the phototransformed SV phase is not stable below 5.5 GPa, and changes into the former MV phase after a long dead time of $\ensuremath{\sim}{10}^{4}$ s.

Photoinduced phase transition in a mixed-valence gold complex

The sol–gel process has been applied successfully to the preparation of small-sized CuCl-doped silica glass with a significant quantum-sized effect. Gel synthesized by the hydrolysis of a complex solution of Si(OC2H5)4 and CuCl with an HCl catalyst is heated to 900°C to form fine, cubic CuCl crystals. Above 700°C, absorption peaks observed at ∼370 and ∼380 nm are attributed to the excitation of confined Z1,2 and Z3 excitons, respectively, in the CuCl microcrystals. As the size of the CuCl crystals decreases, exciton energy shifts to the higher-energy side. The resonant third-order nonlinear susceptibility at 77 K is 1.1 × 10−8 esu, which originates from the enhancement by the quantum-sized effect of the exciton.

Preparation and Nonlinear Optical Properties of Quantum-Sized CuCl-Doped Silica Glass by the Sol–Gel Process

Optical reflectivity spectra of La(1-x)Sr(x)MnO(3) (0<=x<=0.30) were measured on cleavage surfaces of single crystals. The optical conductivity $\sigma(w) of ferromagnetic-metal La(0.70)Sr(0.30)MnO(3) is characterized by a Drude-like - but not simple Drude - component with large spectral weight below 1.6 eV, which yields a large effective carrier number N*_eff consistent with the results of Hall coefficient and specific heat measurements. The present result demonstrates that the previous result of "small Drude weight" originates from the damage of the sample surface. The Sr-substitution effect on the electronic structure and the origin of the unconventional $\sigma(w) are also discussed.

https://arxiv.org/pdf/cond-mat/9810035.pdf

Precise Measurement of Optical Reflectivity Spectra Using Defect-Free Surface of La(1-x)Sr(x)MnO(3): Evidence Against Extremely Small Drude Weight

Cu 2+ -containing SiO 2 and Al 2 O 5 · 9SiO 2 glasses were prepared by the sol-gel method and heated under reducing conditions to precipitate small-sized Cu and Cu 2 O erystals. Cu 2+ ions incorporated in SiO 2 glass were reduced by heating in N 2 to precipitate Cu 2 O and in H 2 to precipitate Cu microcrystals with diameters of about 5 to 15 nm. Microcrystalline Cu-precipitated glass showed an optical absorption band at 560 nm and its third-order nonlinear susceptibility was 1.25 × 10 −10 esu, which originated from the enhancement by the surface plasmon resonance of Cu particles. In contrast, Cu 2+ ions incorporated in Al 2 O 3 · 9SiO 2 glass remained unchanged after heating in the reducing gas atmospheres.

Cu microcrystals in sol-gel derived glasses

Interrelation between orbital polarization and magnetic structure in bilayer manganites

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