The metal-nonmetal transition in NiS studied by the Mössbauer effect of 57Fe

Mössbauer spectra of ⁵⁷Fe impurities in α NiS show an abrupt collapse of the hyperfine splitting at T_t = 260 K, the nonmetal-metal transition; the extrapolated Néel point is ～420 K. Below T_t, it appears that iron adjacent to a vacancy is low-spin. There us evidence of substantial d-electrons delocalisation above T_t. β NiS does not order magnetically down to 4 K.     

Complete 1H and 13C NMR spectral characterization of 1,6-dioxapyrene and related compounds. An unusual coupling interaction through hydrogen bond in three precursors

The ¹H and ¹³C nmr studies of 1,6-dioxapyrene show the disruption of extended delocalization of the π electrons in this recently synthesized heterocyclic skeleton. A surprising coupling interaction through hydrogen bonding was detected in the precursors bearing formyl and hydroxyl groups in peri positions.     

Hypersonic attenuation near Hc1 in superconducting niobium

Results are reported of hypersonic attenuation at 9 GHz near H_c1 in niobium. We observe a break in the variation of attenuation with applied magnetic field, associated with the existence of the intermediate mixed state.     

Experimental study of Raman scattering by NaI crystals containing F centers

Experimental Raman spectra of Na I containing F-centers are described and compared to the calculated spectra, in the off-resonance approximation. The position of the strong resonant mode, almost of A_1g symmetry, is interpreted using a decrease of 67% in the longitudinal force constant between the F-center and its nearest neighbours and of 20% between the nearest and the fourth neighbours.     

Experimental evidence of one-dimensional plasma modes in superconducting thin wires

We have studied niobium superconducting thin wires deposited onto a SrTiO3 substrate. By measuring the reflection coefficient of the wires, resonances are observed in the superconducting state in the 130 MHz to 4 GHz range. They are interpreted as standing wave resonances of one-dimensional plasma modes propagating along the superconducting wire. The experimental dispersion law, omega versus q, presents a linear dependence over the entire wave vector range. The modes are softened as the temperature increases close the superconducting transition temperature. Very good agreement is obtained between our data and the predicted dispersion relation of one-dimensional plasma modes.