Fyzikální ústav Akademie věd ČR

We have investigated the magnetoelectric effect in BiFeO₃ and observed rather a large change of permittivity with magnetic field at high temperatures, where the sample becomes partially conducting due to defects. However, in this case the magnetoelectric effect is not intrinsic, i.e. due to coupling of polarization and magnetization, but due to combination of magnetoresistance and Maxwell-Wagner polarization effect (see S. Kamba et al., Phys. Rev. B 75, 024403 (2007)).

Series of 15 new liquid crystalline compounds have been synthesized and studied composed of non-symmetrical bent-shaped molecules based on a 7-hydroxynaphtalene-2-carboxylic acid, the central naphtalene core being laterally substituted by chlorine or the methyl group. Studies of textures in planar samples, calorimetric study, X-ray diffraction and dielectric measurements enabled to establish mesomorphic properties (ie. phase transitions and sequences of phases) of these compounds. The studied compounds exhibit the antiferroelectric B2 phase and relatively scarce polar columnar phases.  The full text >>

Nanostructured and organic semiconductors form the basis of a new generation of prospective materials for solar cell fabrication. The efficiency of solar cells crucially depends on the speed of long-range charge carrier transport and the understanding of the transport mechanisms in the mentioned materials is a key knowleged for its improvements. We used time-resolved terahertz spectroscopy as a contact-free probe of ultrafast carrier transport. The technique permits to access easily the complex conductivity in the terahertz spectral range with subpicosecond time resolution. The experiments were carried out in a concert with numerical simulations of the conductivity spectra and this allowed us to elucidate the transport mechanisms in a number of complex materials.