Paul Ernest Parris

Electronic structure of La0.7Sr0.3Mn1?xCuxO3 (0.0?x?0.30)

We have investigated the electronic structure of Cu-substituted La0.7Sr0.3MnO3 (LSMO) by x-ray photoelectron spectroscopy and using density functional theory within local spin-density approximations (LSDA) and LSDA+U. We find that there is a coexistence of mixed-valent Cu ions, Cu3+ with Cu2+ dominant, in all Cu-substituted LSMO samples. From a deconvolution of the XPS spectra of Cu-2p3/2, we determined the ratios of Cu2+/Cu3+ and Mn3+/Mn4+, and in turn calculated the change in the tolerance factors of Cu-substituted LSMO. Valence-band photoelectron spectra show that the density of states at the Fermi level is made up mainly of the O-2p and Mn-3d states with a small contribution near EF from the Cu-3d states. We find that LSDA+U calculations for La1/2Sr1/2Mn1−xCuxO3 describe the half-metallicity and ground state ferromagnetic ordering with no evidence of antiferromagnetism for all systems consistent with experimental neutron diffraction data. Two electron transport channels of the major Mn–O–Mn and the minor Cu–O–Cu chains are found. This suggests that the electronic transport behavior of Cu-substituted LSMO systems may be explained by a combination of two different transport mechanisms: (i) a σpd hybridization between the eg states in a majority spin-up Mn-d channel with O-2p orbitals in the Mn–O–Mn chain and (ii) a σpd hybridization between the eg states in a dominant minority spin-down Cu-d channel with O-2p orbitals in the Cu–O–Cu chain. We also find that the half-metallicity of the compounds is lost upon Cu-substitution with a resulting anisotropic electronic transport of the Cu-pair electrons in the basal plane and along the c axis.

Energetic Disorder, Spatial Correlations, and the High-Field Mobility of Injected Charge Carriers in Organic Solids

(a) Department of Physics, University of Missouri-Rolla, Rolla Missouri 65409, USA(b) Department of Physics and Astronomy and Center for Advanced Studies,University of New Mexico, Albuquerque, NM, 87131, USA(Received September 7, 1999)In a large class of disordered organic solids, the observed field and temperature dependence of themobility of photoinjected charge carriers arises from specific statistical features of the disorderedpotential energy landscape through which they move. In materials with polar constituents, energyfluctuations exhibit strong spatial correlations, with deep energetic valleys developing only overlarge length scales. We present a scaling analysis that shows how the hierarchical field-inducedflattening of fluctuations of different magnitudes gives rise to field dependent (e.g., Poole-Frenkeltype) mobilities characteristic of the spatial correlations from which they arise.

Classical Motion in Force Fields with Short Range Correlations

We study the long time motion of fast particles moving through time-dependent random force fields with correlations that decay rapidly in space, but not necessarily in time. The time dependence of the averaged kinetic energy 〈p2(t)〉/2 and mean-squared displacement 〈q2(t)〉 is shown to exhibit a large degree of universality; it depends only on whether the force is, or is not, a gradient vector field. When it is, 〈p2(t)〉∼t2/5 independently of the details of the potential and of the space dimension. The stochastically accelerated particle motion is then superballistic in one dimension, with 〈q2(t)〉∼t12/5, and ballistic in higher dimensions, with 〈q2(t)〉∼t2. These predictions are supported by numerical results in one and two dimensions. For force fields not obtained from a potential field, the power laws are different: 〈p2(t)〉∼t2/3 and 〈q2(t)〉∼t8/3 in all dimensions d≥1.

Structure, magnetic, and transport properties of Ti-substituted La 0.7 Sr 0.3 MnO 3

Ti-substituted perovskites

Dispersive aspects of the high-field hopping mobility of molecularly doped solids with dipolar disorder

{\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}

Low-field hopping among randomly-distributed sites with uncorrelated energetic disorder

with

Thermal Runaway in Ceramics Arising from the Temperature Dependence of the Thermal Conductivity

0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.20

Traversal times for random walks on small-world networks

, were investigated by neutron diffraction, magnetization, electric resistivity, and magnetoresistance (MR) measurements. All samples show a rhombohedral structure (space group

Normal Transport Properties in a Metastable Stationary State for a Classical Particle Coupled to a Non-Ohmic Bath

R\overline{3}c

Structural, magnetic, and transport properties of Zr-substituted La0.7Sr0.3MnO3

) from 10 K to room temperature. At room temperature, the cell parameters