Abstract-Vibrational states of nano-confined water molecules in beryl investigated by first-principles calculations and optical experiments

M. A. Belyanchikov,  E. S. Zhukova,  S. Tretiak,  A. Zhugayevych,  M. Dressel,  F. Uhlig,  J. Smiatek,  M. Fyt,   V. G. Thomas, B. P. Gorshunov

http://pubs.rsc.org/en/content/articlelanding/2017/cp/c7cp06472a/unauth#!divAbstract

Using quantum mechanical calculations within density functional theory, we provide a comprehensive analysis of infrared-active excitation of water molecules confined in nanocages of a beryl crystal lattice. We calculate infrared-active modes including the translational, librational, and mixed-type resonances of regular and heavy water molecules. The results are compared to the experimental spectra measured for the two principal polarizations of the electric field: parallel and perpendicular to the crystallographic c-axis. Good agreement is achieved between calculated and measured isotopic shifts of the normal modes. We analyze the vibrational modes in connection with the structural characteristics and arrangements of water molecules within the beryl crystal. Specific atomic displacements are assigned to each experimentally detected vibrational mode resolving the properties of nano-confined water on scales not accessible by experiments. Our results elucidate the applicability and efficiency of a combined experimental and computational approach for describing and an in-depth understanding of nano-confined water, and pave the way for future studies of more complex systems.

Abstract-Terahertz spectroscopy of low-energy excitations in E u 0.42 S r 0.58 Mn O 3

L. S. Kadyrov, E. S. Zhukova, V. I. Torgashev, T. Zhang, Z. V. Gagkaeva, M. Dressel, and B. P. Gorshunov

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.245120

The origin of low-energy excitations in the polycrystalline $E{u}_{0.42}S{r}_{0.58}\mathrm{Mn}{O}_3$ manganite is explored by terahertz and infrared spectroscopies. The transition from the charge and/or orbital to antiferromagnetic order ($T_N=130-140K$) is seen as smooth (spread over a temperature range from 50 to 100 K) decrease of free-carrier conductivity with the activation energy change from 86 meV (high temperatures) to 0.52 meV (low temperatures). A broad relaxation is observed at around $10c{m}^{-1}$ which we associate with the dynamics of free charge carriers in the presence of random localizing potential. We discover an absorption resonance at $\approx 50c{m}^{-1}$ below $T_N$ that is assigned to the formation of hybridized “acoustic phonon-magnon” quasiparticles.

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Abstract-Dielectric properties of semi-insulating Fe-doped InP in the terahertz spectral region

L. N. Alyabyeva, E. S. Zhukova, M. A. Belkin,  B. P. Gorshunov


https://www.nature.com/articles/s41598-017-07164-1?WT.feed_name=subjects_physics


We report the values and the spectral dependence of the real and imaginary parts of the dielectric permittivity of semi-insulating Fe-doped InP crystalline wafers in the 2–700 cm−1 (0.06–21 THz) spectral region at room temperature. The data shows a number of absorption bands that are assigned to one- and two-phonon and impurity-related absorption processes. Unlike the previous studies of undoped or low-doped InP material, our data unveil the dielectric properties of InP that are not screened by strong free-carrier absorption and will be useful for designing a wide variety of InP-based electronic and photonic devices operating in the terahertz spectral range.