Lattice dynamics in the intermetallic LaFeSi and the derived superconducting compounds LaFeSiH and LaFeSiO
Résumé
The intermetallic LaFeSi and the derived superconducting compounds LaFeSiH and LaFeSiO have been investigated by polarized Raman spectroscopy. The frequency and symmetry of the Raman phonons modes are well-reproduced by ab-initio calculations. The ionic character of the spacer in this series of compounds and its coupling with the FeSi layers as compared to As-based compounds are discussed. Already at room temperature, Fano-shape modes are reported in the A1g channel while an intriguing doubling of the Fe-based B1g phonon is measured in LaFeSiH. Origins of these observations are discussed based on electron diffraction data and the different scenarios for the origin of such splitting are explored. Furthermore, there is no signature of a structural transition nor long range magnetic ordering in LaFeSiH down to 9 K.