Raman signatures of charge ordering in K0.3WO3

We present polarization- and temperature-dependent Raman spectroscopic study of hexagonal tungsten bronze, K0.3WO3. The observed asymmetry in phonon line shapes indicate the presence of strong lattice anharmonicity arising due to the nonstoichiometry of the material. We observed a broad multipeak Raman feature at low frequency due to the local modes of K atoms known as local structural excitations. The observed vibrational features indicate a second-order phase transition around T=200 K accompanied by a frequency softening of low-frequency phonon modes. The observed phonon anomalies hint a physical picture involving a continuous symmetry change toward a charge-ordered state below 200 K. These observations indicate that K0.3WO3 may exhibit a weak charge-density-wave ground state at low temperatures.

Static magnetic susceptibility, crystal field and exchange interactions in rare earth titanate pyrochlores

The experimental temperature dependence (T = 2–300 K) of single crystal bulk and site susceptibilities of rare earth titanate pyrochlores R2Ti2O7 (R = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) is analyzed in the framework of crystal field theory and a mean field approximation. Analytical expressions for the site and bulk susceptibilities of the pyrochlore lattice are derived taking into account long range dipole–dipole interactions and anisotropic exchange interactions between the nearest neighbor rare earth ions. The sets of crystal field parameters and anisotropic exchange coupling constants have been determined and their variations along the lanthanide series are discussed.

PL oscillations in Cd1-xMnxTe

A new magneto-optical effect is described in the present paper. The local sample heating induced by a focused laser beam of 100 mW power results in chaotic oscillations of the whole excitonic part of the photoluminescence (FL) spectrum of Cd1-xMnxTe (x = 0.095). The spectral region of the PL oscillations coincides with the range of the expected excitonic emissions when the magnetic field is varied from 0 to 10 T. The PL oscillations observed at the low magnetic field (0.1 T) have a different character. Then only the PL intensity changes chaotically and not the PL band position. An intuitive explanation of the observed oscillations is given