Evidence for charge orbital and spin stripe order in an overdoped manganite

We present diffraction data on a single-layered manganite La(0.42)Sr(1.58)MnO4 with hole doping (x>0.5). Overdoped La(0.42)Sr(1.58)MnO4 exhibits a complex ordering of charges, orbitals and spins. Single crystal neutron diffraction experiments reveal three incommensurate and one commensurate order parameters to be tightly coupled. The position and the shape of the distinct superstructure scattering points to a stripe arrangement in which ferromagnetic zigzag chains are disrupted by additional Mn4+ stripes

Orbital polaron lattice formation in lightly doped La1-xSrxMnO3

By resonant x-ray scattering at the Mn K-edge on La7/8Sr1/8MnO3, we show that an orbital polaron lattice (OPL) develops at the metal-insulator transition of this compound. This orbital reordering explains consistently the unexpected coexistence of ferromagnetic and insulating properties at low temperatures, the quadrupling of the lattice structure parallel to the MnO2-planes, and the observed polarization and azimuthal dependencies. The OPL is a clear manifestation of strong orbital-hole interactions, which play a crucial role for the colossal magnetoresistance effect and the doped manganites in general

Orbiton-mediated multi-phonon scattering in La1−x_{1-x}Srx_xMnO3_3

We report on Raman scattering measurements of single crystalline La$_{1-x}$Sr$_x$MnO$_3$ ($x$=0, 0.06, 0.09 and 0.125), focusing on the high frequency regime. We observe multi-phonon scattering processes up to fourth-order which show distinct features: (i) anomalies in peak energy and its relative intensity and (ii) a pronounced temperature-, polarization-, and doping-dependence. These features suggest a mixed orbiton-phonon nature of the observed multi-phonon Raman spectra.Comment: 6pages, 6figures, submitted to PR

Pressure-induced melting of the orbital polaron lattice in La1-xSrxMnO3

We report on the pressure effects on the orbital polaron lattice in the lightly doped manganites $\mathrm{La_{1-x}Sr_xMnO_{3}}$, with $x\sim 1/8$. The dependence of the orbital polaron lattice on $negative$ chemical pressure is studied by substituting Pr for La in $\mathrm{(La_{1-y}Pr_y)_{7/8}Sr_{1/8}MnO_{3}}$. In addition, we have studied its hydrostatic pressure dependence in $\mathrm{(La_{0.9}Pr_{0.1})_{7/8}Sr_{1/8}MnO_{3}}$. Our results strongly indicate that the hopping $t$ significantly contributes to the stabilization of the orbital polaron lattice and that the orbital polarons are ferromagnetic objects which get stabilized by local double exchange processes. The analysis of short range orbital correlations and the verification of the Grueneisen scaling by hard x-ray, specific heat and thermal expansion data reinforces our conclusions.Comment: 7 figure

Crystal and magnetic structure of La_{1-x}Sr_{1+x}MnO_{4} : role of the orbital degree of freedom

The crystal and magnetic structure of La_{1-x}Sr_{1+x}MnO_4 (0<x<0.7) has been studied by diffraction techniques and high resolution capacitance dilatometry. There is no evidence for a structural phase transition like those found in isostructural cuprates or nickelates, but there are significant structural changes induced by the variation of temperature and doping which we attribute to a rearrangement of the orbital occupation.Comment: 8 pages, 6 figures, submitted to PR

Existence of orbital polarons in ferromagnetic insulating La1−x_{1-x}Srx_xMnO3_{3} (0.11<x<<x<0.14) evidenced by giant phonon softening

We present an inelastic light scattering study of single crystalline (La$_{1-y}$Pr$_y$)$_{1-x}$Sr$_{x}$MnO$_3$ ($0\leq x\leq0.14$,$y=0$ and $x=1/8$,$0\leq y\leq0.5$). A giant softening up to 20 - 30 cm$^{-1}$ of the Mn-O breathing mode has been observed only for the ferromagnetic insulating (FMI) samples ($0.11\leq x \leq 0.14$) upon cooling below the Curie temperature. With increasing Pr-doping the giant softening is gradually suppressed. This is attributed to a coupling of the breathing mode to orbital polarons which are present in the FMI phase.Comment: 4 pages, 5 figure

Устойчивость бортов карьеров в сложноструктурном массиве мягких пород

Изложены результаты исследований, на основе которых были установлены геомеханические закономерности устойчивого состояния откосов и бортов карьеров с учетом сложной геологической структуры, гидрогеологических характеристик и нагрузок горно-транспортного оборудования. Материал монографии может быть использован в учебном процессе при изложении лекций по дисциплинам «Механика грунтов», «Механика горных пород», «Охрана земной поверхности», при изучении вопросов геомеханической оценки устойчивости естественных и техногенных откосов, прогноза оползнеопасных ситуаций, для дальнейшей разработки и усовершенствования методов анализа напряженно-деформированного состояния массива мягких вскрышных пород, а также специалистами научно- исследовательских учреждений для разработки проектной документации

Evidence for a Low-Spin to Intermediate-Spin State Transition in LaCoO3

We present measurements of the magnetic susceptibility and of the thermal expansion of a LaCoO$_3$ single crystal. Both quantities show a strongly anomalous temperature dependence. Our data are consistently described in terms of a spin-state transition of the Co$^{3+}$ ions with increasing temperature from a low-spin ground state to an intermediate-spin state without (100K - 500K) and with (>500K) orbital degeneracy. We attribute the lack of orbital degeneracy up to 500K to (probably local) Jahn-Teller distortions of the CoO$_6$ octahedra. A strong reduction or disappearance of the Jahn-Teller distortions seems to arise from the insulator-to-metal transition around 500 K.Comment: an error in the scaling factor of Eq.(4) and consequently 2 values of table I have been corrected. The conclusions of the paper remain unchanged. See also: C. Zobel et al. Phys. Rev. B 71, 019902 (2005) and J. Baier et al. Phys. Rev. B 71, 014443 (2005

Bridging charge-orbital ordering and Fermi surface instabilities in half-doped single-layered manganite La_0.5Sr_1.5MnO_4

Density waves are inherent to the phase diagrams of materials that exhibit unusual, and sometimes extraordinarily useful properties, such as superconductivity and colossal magnetoresistance. While the pure charge density waves (CDW) are well described by an itinerant approach, where electrons are treated as waves propagating through the crystal, the charge-orbital ordering (COO) is usually explained by a local approach, where the electrons are treated as localized on the atomic sites. Here we show that in the half-doped manganite La0.5Sr1.5MnO4 (LSMO) the electronic susceptibility, calculated from the angle-resolved photoemission spectra (ARPES), exhibits a prominent nesting-driven peak at one quarter of the Brillouin zone diagonal, that is equal to the reciprocal lattice vector of the charge-orbital pattern. Our results demonstrate that the Fermi surface geometry determines the propensity of the system to form a COO state which, in turn, implies the applicability of the itinerant approach also to the COO