Tuning the Multiferroic Properties of BiFeO_{3} under Uniaxial Strain.

More than twenty years ago, multiferroic compounds combining in particular magnetism and ferroelectricity were rediscovered. Since then, BiFeO_{3} has emerged as the most outstanding multiferroic by combining at room temperature almost all the fundamental or applicative properties that may be desired: electroactive spin wave excitations called electromagnons, conductive domain walls, or a low band gap of interest for magnonic devices. All these properties have so far only been discontinuously strain engineered in thin films according to the lattice parameter imposed by the substrate.

Disentangling Lattice and Electronic Instabilities in the Excitonic Insulator Candidate Ta_{2}NiSe_{5} by Nonequilibrium Spectroscopy.

Ta_{2}NiSe_{5} is an excitonic insulator candidate showing the semiconductor or semimetal-to-insulator (SI) transition below T_{c}=326  K. However, since a structural transition accompanies the SI transition, deciphering the role of electronic and lattice degrees of freedom in driving the SI transition has remained controversial. Here, we investigate the photoexcited nonequilibrium state in Ta_{2}NiSe_{5} using pump-probe Raman and photoluminescence spectroscopies.

Nematic-Fluctuation-Mediated Superconductivity Revealed by Anisotropic Strain in Ba(Fe_{1-x}Co_{x})_{2}As_{2}.

Anisotropic strain is an external field capable of selectively addressing the role of nematic fluctuations in promoting superconductivity. We demonstrate this using polarization-resolved elasto-Raman scattering by probing the evolution of nematic fluctuations under strain in the normal and superconducting state of the paradigmatic iron-based superconductor Ba(Fe_{1-x}Co_{x})_{2}As_{2}. In the parent compound BaFe_{2}As_{2} we observe a strain-induced suppression of the nematic susceptibility which follows the expected behavior of an Ising order parameter under a symmetry breaking field.

Elastic and magnetoelastic properties of TbMnOsingle crystal by nanosecond time resolved acoustics and first-principles calculations.

Time resolved pump and probe acoustics and first-principles calculations were employed to assess elastic properties of the TbMnOperovskite manganite having orthorhombic symmetry. Measuring sound velocities of bulk longitudinal and shear acoustic waves propagating along at least two different directions in the high symmetry planes (100), (010) and (001), provided a powerful mean to selectively determine the six diagonal elastic constants= 227 GPa,= 349 GPa,= 274 GPa,= 71 GPa,= 57 GPa,= 62 GPa. Among the three remaining off-diagonal ones,= 103 GPa was determined with a bissectrice direction.

Possible observation of the signature of the bad metal phase and its crossover to a Fermi liquid in κ-(BEDT-TTF)Cu(NCS) bulk and nanoparticles by Raman scattering.

κ-(BEDT-TTF)Cu(NCS) has been investigated by Raman scattering in both bulk and nanoparticle compounds. Phonon modes from 20 to 1600 cm have been assigned. Focusing on the unexplored low frequency phonons, a plateau in frequencies is observed in the bulk phonons between 50 and 100 K and assigned to the signature of the bad metal phase.