Infrared reflectivity of the phonon spectra in multiferroic TbMnO_3

摘要

We measured the temperature-dependent infrared reflectivity spectra of TbMnO_3 with the electric field of light polarized along each of the three crystallographic axes. We analyzed the effect, on the phonon spectra, of the different phase transitions occurring in this material. We show that the antiferromagnetic transition at T_N renormalizes the phonon parameters along the three directions. Our data indicate that the electromagnon, observed along the a direction, has an important contribution in building the dielectric constant. Only one phonon, observed along the c axis, has anomalies at the ferroelectric transition. This phonon is built mostly from Mn vibrations, suggesting that Mn displacements are closely related to the formation of the ferroelectric order.