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Measurements of the real sigma(1) and imaginary sigma(2) part of the conductivity were performed in optimally doped BaFe1.9Ni0.1As2 and overdoped BaFe1.88Ni0.12As2 crystals in the frequency range 20 MHz-1.5 GHz using a single coil technique. The temperature dependence of the London penetration depth follows a T-2 law. The conductivity sigma(1) increases with decreasing temperature below T-c, in agreement with the results obtained for the optimally Co doped BaFe2-xCoxAs2 crystals. The increase of sigma(1) in the superconducting state is attributed to a rapidly decrease of the quasiparticle scattering rate. (C) 2014 Elsevier Ltd. All rights reserved.

The d.c. conductivity and attenuation of surface acoustic waves (SAW) have been measured in conducting LB films prepared by the vertical dipping method as a function of temperature. The large attenuation of SAW by the film is due to the electric field coupling loss in the film. The a.c. conductivity calculated from the attenuation data is compared with the d.c. conductivity

We report ultrasonic measurements on the quasi-one-dimensional CuGeO3 compound. The longitudinal elastic constants C33 along the chains (c axis) and C22 along the b axis perpendicular to the chains have been measured. A small value of C22 corresponding to a sound velocity of about 2000m/s has been found. Both elastic constants exhibit a sharp and large decrease (⋍ 10−3) at the spin-Peierls transition T c ⋍ 14.5 K .

Magnetic field dependence of ultrasound velocity in YBa 2 Cu 3 O 7 single crystals and Bi 2 Sr 2 CaCu 2 O 8 textured samples is reported. The high (MHz) and the low (Hz) frequency elastic behaviours of the flux line lattice are compared. The very small frequency dependence observed in a large frequency range is not related easily to a simple model of thermal activation.

Attenuation of acoustical surface waves in the range 100–500 MHz has been measured in sublimed C 60 films. A large attenuation governed by a thermally activated relaxation mechanism having an activation energy of 0.07 eV is observed around 180 K. The ultrasonic results are compared with the NMR and low frequency elastic measurements.

Ultrasonic experiments on superconducting and non-superconducting single crystals of Nd 1.85 Ce 0.15 CuO 4−y are reported. No anomalous behaviour of the sound velocity of the longitudinal mode C 33 and transverse mode C s generated in the basal plane has been observed at the superconducting transition in agreement with the thermodynamic prediction.

(TaSe4)2I is a quasi-1 D conductor which undergoes a Peierls transition at Tp = 260 K [1]. Phonon softening at 2kF (Fermi momentum) induces lattice modulations associated with an electron charge density wave (CDW). Elastic singularities at the Peierls transition are not yet well understood [2]. The associated singularity in the sound velocity examined theoretically by Nakane [3] varies like |T-Tp|−1/2 around Tp.

We report a.c. susceptibility measurements in the diluted magnetic semiconductor Cd 1- x Mn x Te for x = 0.45 and 0.55 between 10 Hz and 6 MHz. The experimental data are interpreted in terms of dynamic scaling laws with a transition temperature T c consistent with the static results.

Dielectric measurements at 9.4 GHz in KCl doped with a concentration of 0.2 at. % OH are reported. The dielectric constant exhibits a relaxational anomaly at temperatures far above that observed in the kilohertz frequency range for the same OH concentration. The results indicate that electric dipole freezing in KCl:OH is governed by a relaxational mechanism.

Monte Carlo simulation of electric dipole correlations in KCl doped with OH at a concentration of 0.2 at.% are reported. Using a classical model the calculated dielectric susceptibility and specific heat show good agreement with the experimental results obtained around the temperature T F corresponding to the maximum of the dielectric dispersion and characterizing the freezing of the electric dipole system.

Sound velocity and attenuation results on YBa 2 Cu 3 O 7−δ single crystals are reported. Softening of the longitudinal mode C L along the [110] direction has been observed around the superconducting transition T c . Below T c a relaxation mechanism is responsible for the anomalous behaviour of the C L mode. Measurements of the shear modulus (C 11 -C 12 )/2 are reported.

Sound velocity results on YBa 2 Cu 3 O 7-δ and GdBa 2 Cu 3 O 7-δ single crystals are reported. Discontinuities in the temperature derivatives of the longitudinal and shear sound velocities are observed at the superconducting transition T c . Hardening in both longitudinal (C 33 ) and shear (C 44 ) modes is observed below T c . Estimations of the second stress derivatives of T c are evaluated using a mean field thermodynamics analysis. A second phase transition is observed around 108 K.