Unconventional Optical Response in Engineered Au-Ag Nanostructures

This article describes the optical properties of nanostructures composed of silver particles embedded into a gold matrix. In previous studies these materials were shown to exhibit temperature dependent transitions to a highly conductive and strongly diamagnetic state. Here we describe the anomalous optical properties of these nanostructures. Most notably, these materials fail to obey Mie theory and exhibit an unconventional resonance with a maximum at about 4 eV, while the usual gold and silver localized surface plasmon resonances are suppressed. This effect implies a significant deviation from the bulk dielectric functions of gold and silver. We further resolved this resonance into its absorbance and scattering sub-parts. It is observed that the resonance is largely comprised of scattering, with negligible losses even at ultraviolet frequencies.

Unconventional Optical Response in Engineered Au-Ag Nanostructures

This article describes the optical properties of nanostructures composed of silver particles embedded into a gold matrix. In previous studies these materials were shown to exhibit temperature dependent transitions to a highly conductive and strongly diamagnetic state. Here we describe the anomalous optical properties of these nanostructures. Most notably, these materials fail to obey Mie theory and exhibit an unconventional resonance with a maximum at about 4 eV, while the usual gold and silver localized surface plasmon resonances are suppressed. This effect implies a significant deviation from the bulk dielectric functions of gold and silver. We further resolved this resonance into its absorbance and scattering sub-parts. It is observed that the resonance is largely comprised of scattering, with negligible losses even at ultraviolet frequencies.

Structural Studies of Iron(III) Complexes with N4O2 Coordination Sphere

The Spin-Crossover (SCO) phenomenon implicates a switchable between a low-spin (LS) diamagnetic state, which is stable at low temperatures and a paramagnetic high-spin state (HS), which is stable at higher temperatures. This transition is generated by an external perturbation such as temperature, pressure or light. In general, the switching process in solid-state systems is controlled by cooperative intermolecular interactions. The correlation of structure with physical properties is crucial to the identification of these interactions and ultimately the understanding of the complex processes that control the SCO phenomenon[1]. With the aim of developing new SCO materials, we carried out the syntheses and crystal structure analysis of seven iron(III) complexes, mixing 5-bromo-salicylaldehyde or 5-chloro-salicylaldehyde and ethylendiamine with iron(III) chloride and/or ammonium hexafluorophosphate solutions by slow diffusion or reflux in methanol or 2-propanol (figure 1). The crystal structures show the iron(III) centre is hexacoordinated (FeN4O2) and the coordination polyhedron can be described as a distorted octahedron formed by the 4 N atoms of the ethylenediamine fragment and 2 hydroxyl O atoms from the salicylaldehyde fragment, this distortion was evaluated at 120 and 298 K, the major distortion were observed in complexes [2]+ PF6–· MeOH, [2]+ PF6–·iPrOH and [1]+ PF6–·MeOH, which is characteristic in HS states, while the complexes [2]+ Cl–·iPrOH, [1]+ PF6–·iPrOH [2]+ and [2]+ClO4–, shows a minor distortion according to LS states. On the other hand, [1]+ClO4– is a SCO complex with a typical geometry for both spin states at 120 K (LS) and 298 K (HS). Finally, we studied the intermolecular interactions using Crystal Explorer Software[2] between the iron complexes, the counterion and/or the solvate molecule, for instance, in the [2]+PF6–·MeOH complex, the most remarkable feature observed are Br···Br intermolecular interactions (figure 2). ACKNOWLEDGMENTS: FONDECYT N01130640, FONDEQUIP EQM120095 and Beca CONICYT folio 21130944

ELECTROSTATIC FIELD IN SUPERCONDUCTORS I: OPEN QUESTIONS

The electrostatic field in superconductors in the equilibrium diamagnetic state is discussed. On recent experimental data we demonstrate that the electrostatic field in superconductors is still far from being understood. Then we present the elementary ideas based on the balance of forces.

Collapse of the Static Magnetization in Anisotropic Hard Superconductors

The suppression (collapse) of the static magnetization of an anisotropic hard superconductor under effect of ac magnetic fields was studied experimentally and theoretically. The measurements were carried out in mutually orthogonal dc and ac magnetic fields, [Formula: see text] and [Formula: see text]. Both fields were parallel to the sample surface. Superconducting Y-123 plate-like single crystals were cut from a textured ingot in such a way that the c axis was in the sample plane. The amplitude of the ac field that suppresses completely the static magnetization was shown to be dependent on the orientation of the magnetic fields with respect to the crystallographic axes of the sample. The dynamics of the collapse of the magnetization was investigated. In some cases, the magnetic moment was found to change non-monotonically with the increase of the amplitude of the ac magnetic field. An unusual phenomenon of the transition of the superconductor from the paramagnetic to diamagnetic state induced by the transverse ac field is discovered. The observed results are interpreted within the framework of the critical state model generalized to the anisotropic case.

Article

Electroreduction of the 2,5-thiophene-bridged bis(1,2,3,5-diselenadiazolylium) salt [T-2,5-Se][SbF6]2 in acetonitrile, at a Pt wire and in the presence of iodine, affords a highly conductive ( sigma = 102 S cm-1 at 293 K) 1:1 charge-transfer (CT) salt [T-2,5-Se][I], the crystal structure of which has been determined by single-crystal X-ray diffraction. The crystals belong to the orthorhombic space group Fm2m, a = 3.544(2), b = 10.9808(16), c = 31.464(5) Å , V = 1224.5(7) Å 3. The structure consists of perfectly superimposed pi -stacks of molecular units bridged by columns of disordered iodines. This packing motif is similar to that of the related 1,3-benzene-bridged derivative [1,3-Se][I], but the lateral intermolecular Se···Se interactions linking adjacent pi -stacks are considerably shorter, indicative of a more isotropic electronic structure for [T-2,5-Se][I]. Magnetic susceptibility measurements on [T-2,5-Se][I] nonetheless indicate a phase transition to a diamagnetic state near 200 K, behaviour similar to that observed for [1,3-Se][I]. The electronic structures and transport properties of the two compounds are discussed in the light of extended Hückel band-structure calculations.Key words: diselenadiazolyl, diradical, charge-transfer salt, magnetic susceptibility, crystal structure.