Low-energy Mott-Hubbard excitations in LaMnO_3 probed by optical ellipsometry (2009)
Kovaleva, N. N., Oles, Andrzej M., Balbashov, A. M., Maljuk, A., Argyriou, D. N., Khaliullin, G., ...
We present a comprehensive ellipsometric study of an untwinned, nearly stoichiometric LaMnO_3 crystal in the spectral range 1.2-6.0 eV at temperatures 20 K < T < 300 K. The complex dielectric...
Low-energy Mott-Hubbard excitations in LaMnO$_3$ (2009)
Kovaleva, N. N., Oles, Andrzej M., Balbashov, A. M., Maljuk, A., Argyriou, D. N., Khaliullin, G., ...
More discussion from the theory is suggested
Electron-phonon interaction and spectral weight transfer in Fe$_{1-x}$Co$_{x}$Si (2009)
Menzel, D., Popovich, P., Kovaleva, N. N., Schoenes, J., Doll, K., Boris, A. V.
A comprehensive ellipsometric study was performed on Fe$_{1-x}$Co$_{x}$Si single crystals in the spectral range from 0.01 eV to 6.2 eV. Direct and indirect band gaps of 73 meV and 10 meV,...
Ferromagnetism and lattice distortions in the perovskite YTiO§3. (2009)
Knafo, W., Meingast, C., Boris, A.V., Popovich, P., Kovaleva, N.N., Yordanov, P., ...
Physical Review B, 79(2009) S.054431/1-10
Ferromagnetism and Lattice Distortions in the Perovskite YTiO$_3$ (2008)
Knafo, W., Meingast, C., Löhneysen, H. V., Boris, A. V., Popovich, P., Kovaleva, N. N., ...
The thermodynamic properties of the ferromagnetic perovskite YTiO$_3$ are investigated by thermal expansion, magnetostriction, specific heat, and magnetization measurements. The low-temperature...
Dipole-active optical phonons in YTiO_3: ellipsometry study and lattice-dynamics calculations (2008)
Kovaleva, N. N., Boris, A. V., Capogna, L., Gavartin, J. L., Popovich, P., Yordanov, P., ...
The anisotropic complex dielectric response was accurately extracted from spectroscopic ellipsometry measurements at phonon frequencies for the three principal crystallographic directions of an...
Signatures of Electronic Correlations in Optical Properties of LaFeAsO$_{1-x}$F$_x$ (2008)
Boris, A. V., Kovaleva, N. N., Seo, S. S. A., Kim, J. S., Popovich, P., Matiks, Y., ...
Spectroscopic ellipsometry is used to determine the dielectric function of the superconducting LaFeAsO$_{0.9}$F$_{0.1}$ ($T_c$ = 27 K) and undoped LaFeAsO polycrystalline samples in the wide range...
Optical response of ferromagnetic YTiO₃ studied by spectral ellipsometry (2008)
Kovaleva, N. N., Boris, A. V., Yordanov, P., Maljuk, A., Brücher, E., Strempfer, J., ...
We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO₃ single crystal with ferromagnetic Curie temperature TC=30...
Optical response of ferromagnetic YTiO₃ studied by spectral ellipsometry (2008)
Kovaleva, N. N., Boris, A. V., Yordanov, P., Maljuk, A., Brücher, E., Strempfer, J., ...
We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO₃ single crystal with ferromagnetic Curie temperature TC=30...
Optical response of ferromagnetic YTiO_3 studied by spectral ellipsometry (2007)
Kovaleva, N. N., Boris, A. V., Yordanov, P., Maljuk, A., Brüchner, E., Strempfer, J., ...
We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO_3 single crystal with ferromagnetic Curie temperature T_C =...
Infrared Optical Properties of La0.7Ca0.3MnO3 Epitaxial Films (2004)
Boris, A. V., Kovaleva, N. N., Bazhenov, A. V., Samoilov, A. V., Yeh, N. C., Vasquez, R. P.
The reflectance of La0.7Ca0.3MnO3 epitaxial films on perovskite substrates with a range of lattice constants is studied in the frequency range of 50 cm-1 - 5000cm-1. The complex dielectric functions...
Infrared Optical Properties of La0.7Ca0.3MnO3 Epitaxial Films (2004)
Boris, A. V., Bazhenov, A. V., Kovaleva, N. N., Samoilov, A. V., Yeh, N. C., Vasquez, R. P.
Yeh, N. C., Vasquez, R. P., Wei, J. Y. T., Fu, C. C., Beach, G., Huynh, J., ...
The relevance of lattice distortion, polaron conduction, and double-exchange interaction to the occurrence of colossal magnetoresistance (SMR) is investigated by comparing the physical properties of...
Spin-controlled Mott-Hubbard bands in LaMnO_3 probed by optical ellipsometry (2004)
Kovaleva, N. N., Boris, A. V., Bernhard, C., Kulakov, A., Pimenov, A., Balbashov, A. M., ...
Spectral ellipsometry has been used to determine the dielectric function of an untwinned crystal of LaMnO_3 in the spectral range 0.5-5.6 eV at temperatures 50 K < T < 300 K. A pronounced...
In-Plane Spectral Weight Shift of Charge Carriers in $YBa_2Cu_3O_{6.9}$ (2004)
Boris, A. V., Kovaleva, N. N., Dolgov, O. V., Holden, T., Lin, C. T., Keimer, B., ...
The temperature dependent redistribution of the spectral weight of the $CuO_2$ plane derived conduction band of the $YBa_2Cu_3O_{6.9}$ high temperature superconductor (T_c = 92.7 K) was studied with...
Charge ordering and magneto-polarons in Na$_{0.82}$CoO$_2$ (2004)
Bernhard, C., Boris, A. V., Kovaleva, N. N., Khaliullin, G., Pimenov, A., Yu, L., ...
Using spectral ellipsometry, we have measured the dielectric function of a Na$_{0.82(2)}$CoO$_2$ crystal that exhibits bulk antiferromagnetism with T$_{N}$=19.8 K. We identify two prominent...
c-axis lattice dynamics in Bi-based cuprate superconductors (2004)
Kovaleva, N. N., Boris, A. V., Holden, T., Ulrich, C., Liang, B., Lin, C. T., ...
We present the results of a systematic study of the c-axis lattice dynamics in single-layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212), and trilayer Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate...
Bernhard, C., Holden, T., Boris, A. V., Kovaleva, N. N., Pimenov, A. V., Humlíček, J., ...
We observe a large and anomalous oxygen isotope effect on the a-axis component of the far-infrared electronic response of detwinned (YBa2Cu3O6.9)-O-16,18. For O-18 a pronounced low-energy electronic...
Infrared optical properties of the spin-1/2 quantum magnet TiOCl (2004)
Caimi, G., Degiorgi, L., Kovaleva, N. N., Lemmens, P., Chou, F. C.
We report results on the electrodynamic response of TiOCl, a low-dimensional spin-1/2 quantum magnet that shows a spin gap formation for T
In-Plane Spectral Weight Shift of Charge Carriers in YBa2Cu3O6.9 (2004)
Boris, A. V., Kovaleva, N. N., Dolgov, O. V., Holden, T., Lin, C. T., Keimer, B., ...
The temperature-dependent redistribution of the spectral weight of the CuO2 plane-derived conduction band of the YBa2 Cu-3 O-6.9 high-temperature superconductor (superconducting transition...
Charge Ordering and Magnetopolarons in Na0.82CoO2 (2004)
Bernhard, C., Boris, A. V., Kovaleva, N. N., Khaliullin, G., Pimenov, A., Yu, L., ...
Effect of Na content and hydration on the excitation spectrum of the cobaltite NaxCoO2·yH2O (2004)
Lemmens, P., Gnezdilov, V., Kovaleva, N. N., Sakurai, H., Takayama-Muromachi, E., ...
Spin-Controlled Mott-Hubbard Bands in LaMnO3 Probed by Optical Ellipsometry (2004)
Kovaleva, N. N., Boris, A. V., Bernhard, C., Kulakov, A., Pimenov, A., Balbashov, A. M., ...
Giant phonon softening in the pseudogap phase of the quantum spin system TiOCl (2004)
Lemmens, P., Caimi, G., Degiorgi, L., Kovaleva, N. N., Seidel, A., ...
Bernhard, C., Boris, A.V., Kovaleva, N.N., Pimenov, A.V., Yu, L., Lin, C.T., ...
Internat.Conf.on Strongly Correlated Electron Systems (SCES '04), Karlsruhe, July 26-30, 2004
Lemmens, P., Gnezdilov, V., Kovaleva, N. N., Choi, K. Y., Sakurai, H., Takayama-Muromachi, E., ...
We report on a Raman scattering study on the superconducting cobaltite $Na_xCoO_2\cdot yH_2O$ as function of Na content and hydration (x$\approx$1/3, 3/4 and y$\approx$0, 2/3, 4/3). The observed...
Infrared optical properties of the spin-1/2 quantum magnet $TiOCl$ (2003)
Caimi, G., Degiorgi, L., Kovaleva, N. N., Lemmens, P., Chou, F. C.
We report results on the electrodynamic response of $TiOCl$, a low-dimensional spin-1/2 quantum magnet that shows a spin gap formation for T$
Giant phonon anomalies in the pseudo-gap phase of TiOCl (2003)
Lemmens, P., Choi, K. Y., Caimi, G., Degiorgi, L., Kovaleva, N. N., Seidel, A., ...
We report infrared and Raman spectroscopy results of the spin-1/2 quantum magnet TiOCl. Giant anomalies are found in the temperature dependence of the phonon spectrum, which hint to unusual coupling...
C-axis lattice dynamics in Bi-based cuprate superconductors (2003)
Kovaleva, N. N., Boris, A. V., Munzar, D., Holden, T., Ulrich, C., Tallon, J. L., ...
We present results of a systematic study of the c axis lattice dynamics in single layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212) and trilayer Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate...
Bernhard, C., Holden, T., Boris, A. V., Kovaleva, N. N., Pimenov, A. V., Humlicek, J., ...
We observe an anomalous oxygen isotope effect on the a-axis component of the far-infrared electronic response of detwinned YBa2Cu3$^{16,18}$O$_{6.9}$. For $^{18}$O a pronounced low-energy electronic...
Josephson plasma resonance and phonon anomalies in trilayer Bi§2Sr§2Ca§2Cu§3O§1§0. (2003)
Boris, A.V., Munzar, D., Kovaleva, N.N., Liang, B., Lin, C.T., Dubroka, A., ...
Physical Review Letters, 89(2002) S.277001/1-4
Boris, A. V, Munzar, D., Kovaleva, N. N., Liang, B., Lin, C. T., Dubroka, A., ...
The far-infrared (FIR) c axis conductivity of a Bi2223 crystal has been measured by ellipsometry. Below T$_c$ a strong absorption band develops near 500 cm $^{-1}$, corresponding to a transverse...
Josephson Plasma Resonance and Phonon Anomalies in Trilayer Bi2Sr2Ca2Cu3O10 (2002)
Boris, A. V., Munzar, D., Kovaleva, N. N., Liang, B., Lin, C. T., Dubroka, A., ...
The far-infrared (FIR) c axis conductivity of a Bi2223 crystal has been measured by ellipsometry. Below T-c a strong absorption band develops near 500 cm(-1), corresponding to a transverse Josephson...
Formation and relaxation energies of electronic holes in LaMnO3 crystal (2002)
Kovaleva, N. N., Gavartin, J. L., Shluger, A. L., Boris, A. V., Stoneham, A. M.
We use the Mott-Littleton approach to evaluate the electronic and ionic polarisation energies in LaMnO3 lattice associated with holes localised on both Mn3+ cation and O2- anion. The full lattice...
Optical transitions in non-stoichiometric LaMnO3 identifying the charge-transfer transitions (2002)
Kovaleva, N. N., Gavartin, J. L., Boris, A. V., Stoneham, A. M.
Using the Mott-Littleton approach we examine the energies of a number of fundamental optical transitions, as well as those involving self-trapped holes of Mn4+ and O- in LaMnO3 lattice. The...
Boris, A. V., Bernhard, C., Kovaleva, N. N., Mandal, P., Loidl, A.
We have performed ellipsometric measurements of the infrared dielectric response of RuSr2GdCu2O8 polycrystalline ceramics. The transformation of the Cu-O bending phonon mode at 288 cm(- 1) in the...
Kovaleva, N. N., Gavartin, J. L., Shluger, A. L., Boris, A. V., Stoneham, A. M.
We explore the role of electronic and ionic polarization energies in the physics of "colossal" magnetoresistive (CMR) materials. We use the Mott-Littleton approach to evaluate polarization energies...
Kovaleva, N. N., Gavartin, J. L., Shluger, A. L., Boris, A. V., Stoneham, A. M.
We use the Mott-Littleton approach to evaluate polarisation energies in LaMnO$_3$ lattice associated with holes localized on both Mn$^{3+}$ cation and O$^{2-}$ anion. The full (electronic and ionic)...
Boris, A. V., Mandal, P., Bernhard, C., Kovaleva, N. N., Pucher, K., Hemberger, J., ...
Critical behavior of the infrared reflectivity of RuSr_2GdCu_2O_8 ceramics is observed near the superconducting T_{SC} = 45 K and magnetic T_M = 133 K transition temperatures. The optical...
Boris, A. V., Kovaleva, N. N., Bazhenov, A. V., Rasing, Th., Cheong, S-W., ...
The infrared reflectivity of a $\rm La_{0.67}Ca_{0.33}MnO_3$ single crystal is studied over a broad range of temperatures (78-340 K), magnetic fields (0-16 T), and wavenumbers (20-9000 cm$^{-1}$)....