Temperature-Dependent Infrared Reflectivity Studies of Multiferroic TbMnO_{3}: Evidence for Spin-Phonon Coupling

We have measured near normal incidence far infrared (FIR) reflectivity spectra of a single crystal of TbMnO3 from 10K to 300K in the spectral range of 50 cm$^{-1}$ to 700 cm$^{-1}$. Fifteen transverse optic (TO) and longitudinal optic (LO) modes are identified in the imaginary part of the dielectric function $\epsilon_2$($\omega$) and energy loss function Im(-1/$\epsilon$($\omega$)), respectively. Some of the observed phonon modes show anomalous softening below the magnetic transition temperature T$_N$ (~ 46K). We attribute this anomalous softening to the spin-phonon coupling caused by phonon modulation of the super-exchange integral between the Mn$^{3+}$ spins. The effective charge of oxygen (Z$_O$) calculated using the measured LO-TO splitting increases below T$_N$.Comment: 16 pages, 6 figures, 1 tabl

Magneto optical study of the spin polarized electronic states in multiferroic TbMnO3

The magnetic and electronic properties of multiferroic TbMnO3 in the paramagnetic, antiferromagnetic, sinusoidal, and spiral spin phases were studied by spectral generalized magneto optical ellipsometry. The measurements show a strong anisotropy of the dielectric tensor. A redistribution of spectral weight was observed in the diagonal components of the dielectric tensor for the temperature range from 110 to T N 46 K. In the off diagonal elements, spectral generalized magneto optical ellipsometry shows sensitivity to the antiferromagnetic and ferroelectric phase transitions at T N 46 K and T F 29 K, respectively, and a persistent signal up to 6T

Observation of Frenkel and charge transfer excitons in pentacene single crystals using spectroscopic generalized ellipsometry

<p>We report on the emerging and admixture of Frenkel and charge transfer (CT) excitons near the absorption onset in pentacene single crystals. Using high energy-resolution spectroscopic generalized ellipsometry with in-plane polarization dependence, the excitonic nature of three lowest lying excitations is discussed. Their distinct polarization dependence strongly indicates the presence of both Frenkel and CT types of excitons near the excitation onset. In particular, the peculiar polarization behavior of the second excitation can only be rationalized by taking into account the inherent CT transition dipole moment. This observation has important implications for the pentacene-based optoelectronic devices. (C) 2013 AIP Publishing LLC.</p>

Metal-insulator transition in manganites: Changes in optical conductivity up to 22 eV

10.1103/PhysRevB.78.125110Physical Review B - Condensed Matter and Materials Physics7812-PRBM