arXiv subjects

R. Osborn

Publications and source records attributed to R. Osborn.

46 records · Page 3Linked to original sources

arXiv2002

Glass Transition in the Polaron Dynamics of CMR Manganites

Neutron scattering measurements on a bilayer manganite near optimal doping show that the short-range polarons correlations are completely dynamic at high T, but then freeze upon cooling to a temperature T* 310 K. This glass transition suggests that the paramagnetic/insulating state arises from an inherent orbital frustration that inhibits the formation of a long range orbital- and charge-ordered state. Upon further cooling into the ferromagnetic-metallic state (Tc=114 K), where the polarons melt, the diffuse scattering quickly develops into a propagating, transverse optic phonon.

cond-mat.str-el↗

arXiv2001

Magnetic Correlations and the Anisotropic Kondo Effect in Ce1-xLaxAl3

By combining the results of muon spin rotation and inelastic neutron scattering in the heavy fermion compounds Ce1-xLaxAl3 (0.0 <= x <= 0.2), we show that static magnetic correlations are suppressed above a characteristic temperature, T*, by electronic dissipation rather than by thermal disorder. Below T*, an energy gap opens in the single-ion magnetic response in agreement with the predictions of the Anisotropic Kondo Model. Scaling arguments suggest that similar behavior may underlie the "hidden order" in URu2Si2.

cond-mat.str-el↗

arXiv2001

The Structure of Nanoscale Polaron Correlations in La1.2Sr1.8Mn2O7

A system of strongly-interacting electron-lattice polarons can exhibit charge and orbital order at sufficiently high polaron concentrations. In this study, the structure of short-range polaron correlations in the layered colossal magnetoresistive perovskite manganite, La1.2Sr1.8Mn2O7, has been determined by a crystallographic analysis of broad satellite maxima observed in diffuse X-ray and neutron scattering data. The resulting q=(0.3,0,1) modulation is a longitudinal octahedral-stretch mode, consistent with an incommensurate Jahn-Teller-coupled charge-density-wave fluctuations, that implies an unusual orbital-stripe pattern parallel to the <100> directions.

cond-mat.mtrl-sci↗

arXiv2001

Mixed lattice and electronic states in high-temperature superconductors

Inelastic neutron scattering measurements are presented which show the abrupt development of new oxygen lattice vibrations near the doping-induced metal-insulator transition in La(2-x)Sr(x)CuO(4). A direct correlation is established between these lattice modes and the electronic susceptibility (as measured by photoemission) inferring that such modes mix strongly with charge fluctuations. This electron-lattice coupling can be characterized as a localized one-dimensional response of the lattice to short-ranged metallic charge fluctuations.

cond-mat.supr-con↗

arXiv2001

Phonon Density-of-States in MgB2

We report inelastic neutron scattering measurements of the phonon density-of-states in Mg11B2, which has a superconducting transition at 39.2 K. The acoustic phonons extend in energy to 36 meV, and there are highly dispersive optic branches peaking at 54, 78, 89 and 97 meV. A simple Born-von Karman model is able to reproduce the mode energies, and provides an estimate of the electron-phonon coupling of lambda~0.9. The estimated boron and magnesium contributions to the isotope effect are in qualitative agreement with experiment. The data confirm that a conventional phonon mechanism, with moderately strong electron-phonon coupling, can explain the observed superconductivity.

cond-mat.supr-con↗

arXiv2001

Slow crossover in YbXCu4 intermediate valence compounds

We compare the results of measurements of the magnetic susceptibility Chi(T), the linear coefficient of specific heat Gamma(T)=C(T)/T and 4f occupation number nf(T) for the intermediate valence compounds YbXCu4 (X = Ag, Cd, In, Mg, Tl, Zn) to the predictions of the Anderson impurity model, calculated in the non-crossing approximation (NCA). The crossover from the low temperature Fermi liquid state to the high temperature local moment state is substantially slower in the compounds than predicted by the NCA; this corresponds to the ''protracted screening'' recently predicted for the Anderson Lattice. We present results for the dynamic susceptibility, measured through neutron scattering experiments, to show that the deviations between theory and experiment are not due to crystal field effects, and we present x-ray-absorption fine-structure (XAFS) results that show the local crystal structure around the X atoms is well ordered, so that the deviations probably do not arise from Kondo Disorder. The deviations may correlate with the background conduction electron density, as predicted for protracted screening.

cond-mat.str-el↗

arXiv1999

Observation of Kosterlitz-Thouless spin correlations in the colossally magnetoresistive layered manganite $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$

The spin correlations of the bilayer manganite $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$ have been studied using neutron scattering. On cooling within the paramagnetic state, we observe purely two-dimensional behavior with a crossover to three-dimensional scaling close to the ferromagnetic transition. Below $T_C$, an effective finite size behavior is observed. The quantitative agreement of these observations with the conventional quasi two-dimensional Kosterlitz-Thouless model indicates that the phase transition is driven by the growth of magnetic correlations, which are only weakly coupled to polarons above $T_C$.

cond-mat.str-el↗

arXiv1999

Charge melting and polaron collapse in $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$

X-ray and neutron scattering measurements directly demonstrate the existence of polarons in the paramagnetic phase of optimally-doped colossal magnetoresistive oxides. The polarons exhibit short-range correlations that grow with decreasing temperature, but disappear abruptly at the ferromagnetic transition because of the sudden charge delocalization. The "melting" of the charge ordering as we cool through $T_C$ occurs with the collapse of the quasi-static polaron scattering, and provides important new insights into the relation of polarons to colossal magnetoresistance.

cond-mat.str-el↗

arXiv1999

Phonons and hole localization in La(1.475)Nd(0.4)Sr(0.125)CuO(4)

The phonon densities-of-states of La(1.475)Nd(0.4)Sr(0.125)CuO(4) and La(1.9)Sr(0.1)CuO(4) were measured using inelastic neutron scattering. The ~70 meV phonon band which appears due to hole doping in La(1.9)Sr(0.1)CuO(4) is known to arise from strong electron-lattice coupling. This phonon band is strongly suppressed in the Nd-doped compound for which T_c is also suppressed, establishing a link between in-plane oxygen optical phonons and superconductivity. This suppression is attributed to hole localization which becomes strong near the stripe ordering condition of certain cuprates near x=1/8 and competes with superconductivity.

cond-mat.supr-con↗

arXiv1997

Neutron scattering investigation of magnetic bilayer correlations in $La_{1.2}Sr_{1.8}Mn_2O_7$

Neutron scattering investigations of the paramagnetic correlations in the layered manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$, which exhibits colossal magnetoresistance above the Curie transition at T$_C$ = 112 K, show that spins in neighboring layers within each bilayer are strongly canted at an average angle that is dependent on both the magnetic field and temperature, as predicted by de Gennes. The in-plane correlation length does not diverge at T$_C$, although the magnetic Bragg intensity obeys critical scaling below T$_C$, with the same temperature dependence as the zero-field electrical conductance.

cond-mat.str-el↗