Related papers: Orbital Dimerization and Dynamic Jahn-Teller Effec…
Reflectivity as a function of temperature for the La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) film has been measured across the metal-insulator phase transition. The optical properties and their temperature dependence were determined in the…
The ferroelectric to paraelectric phase transition of multiferroic CaMnTi$_2$O$_6$ has been investigated at high pressures and ambient temperature by second harmonic generation (SHG), Raman spectroscopy, and powder and single-crystal x-ray…
We study the controlled manipulation of the Jahn-Teller metal state of fulleride compounds using nonequilibrium dynamical mean field theory. This anomalous metallic state is a spontaneous orbital-selective Mott phase, which is characterized…
We study a two dimensional, two-band double-exchange model for $e_g$ electrons coupled to Jahn-Teller distortions in the presence of quenched disorder using a recently developed Monte-Carlo technique. In the absence of disorder the…
Dynamics of the main dielectric anomaly in Na1/2Bi1/2TiO3 (NBT) was studied by time-domain THz and microwave spectroscopy, using also previously published data and their new overall fits. Above the dielectric maximum temperature Tm ~ 600 K,…
Evolution of the average and local crystal structure of Ca-doped LaMnO$_{3}$ has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two…
High-pressure infrared transmission measurements on \PhC60 were performed up to 9 GPa over a broad frequency range (200 - 20000 cm$^{-1}$) to monitor the vibrational and electronic/vibronic excitations under pressure. The four fundamental…
The Jahn-Teller distortive transition of \lmo is described by a modified 3-state Potts model. The interactions between the three possible orbits depends both on the orbits and their relative orientation on the lattice. Values of the two…
The interaction of coexisting structural instabilities in multiferroic materials gives rise to intriguing coupling phenomena and extraordinarily rich phase diagrams, both in bulk materials and strained thin films. Here we investigate the…
Mermin-Wagner theorem forbid spontaneous symmetry breaking of spins in one/two-dimensional systems at finite temperature and rules out the stabilization of this ordered state. However, it does not apply to all types of phase transitions in…
We report low-temperature Raman signatures of the Heisenberg quantum magnet Ca$_{10}$Cr$_7$O$_{28}$, showing clear anomalies in phonon mode frequencies and linewidths below $\sim$100 K. This crossover temperature lies in between the…
Raman scattering experiments have been performed on Na_xCoO_2 as function of temperature at the composition x=0.5 where a structural instability and a metal-insulator transition have been observed. Three additional phonon modes are observed…
Studying the nature and consequences of electron-phonon interaction in manganites is an area of intense ongoing research. Here, in an attempt to model charge and orbital ordering in manganites displaying C-type antiferromaganetism, we study…
We have investigated the dynamics of Na ions in amorphous Na2Si2O5, a potential solid electrolyte material for Na-battery. We have employed quasielastic neutron scattering (QENS) technique in the amorphous Na2Si2O5 from 300 to 748 K to…
Structural phase transition studies employing low-temperature transmission electron microscopy, and low-temperature x-ray diffraction have been carried out on nearly stoichiometric ({\delta}=0.01) and off-stoichiometric ({\delta}=0.12)…
A classical model for the lattice distortions of $\lax$ is derived and, in a mean field approximation, solved. The model is based on previous work by Kanamori and involves localized Mn d-electrons (which induce tetragonal distortions of the…
The phonon renormalization across the semiconductor-to-metal crossover in FeSi is investigated by inelastic neutron scattering combined with \textit{ab-initio} lattice dynamical calculations. A significant part of reciprocal space with a…
We report a molecular dynamics study of ab initio quality of the ferroelectric phase transition in crystalline PbTiO3. We model anharmonicity accurately in terms of potential energy and polarization surfaces trained on density functional…
Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ is one of the simplest representatives of the class of lead relaxors and often serves as a model system for more complicated compounds. In this paper we analyse both polarized and depolarized Raman scattering…
Ordering and quantum fluctuations of orbital degrees of freedom are studied theoretically for LaVO$_3$ in spin-C-type antiferromagnetic state. The effective Hamiltonian for the orbital pseudospin shows strong one-dimensional anisotropy due…