3,058 research outputs found
Charge Distribution Near Oxygen Vacancies in Reduced Ceria
Understanding the electronic charge distribution around oxygen vacancies in
transition metal and rare earth oxides is a scientific challenge of
considerable technological importance. We show how significant information
about the charge distribution around vacancies in cerium oxide can be gained
from a study of high resolution crystal structures of higher order oxides which
exhibit ordering of oxygen vacancies. Specifically, we consider the
implications of a bond valence sum analysis of CeO and
CeO. To illuminate our analysis we show alternative
representations of the crystal structures in terms of orderly arrays of
co-ordination defects and in terms of flourite-type modules. We found that in
CeO, the excess charge resulting from removal of an oxygen atom
delocalizes among all three triclinic Ce sites closest to the O vacancy. In
CeO, the charge localizes on the next nearest neighbour Ce atoms.
Our main result is that the charge prefers to distribute itself so that it is
farthest away from the O vacancies. This contradicts \emph{the standard picture
of charge localisation} which assumes that each of the two excess electrons
localises on one of the cerium ions nearest to the vacancy. This standard
picture is assumed in most calculations based on density functional theory
(DFT). Based on the known crystal structure of PrO, we also
predict that the charge in CeO will be found in the second
coordination shell of the O vacancy. Although this review focuses on bulk
cerium oxides our approach to characterising electronic properties of oxygen
vacancies and the physical insights gained should also be relevant to surface
defects and to other rare earth and transition metal oxides.Comment: 20 pages, 23 figures. The replacement file has a new format for the
figures are the document layout but no change in content. v3 has the
following main changes: 1. The abstract and introduction were extensively
revised. 2. Sec. IV was removed. 3. The Conclusion was rewritte
Apparent Violation of the Wiedemann-Franz law near a magnetic field tuned metal-antiferromagnetic quantum critical point
The temperature dependence of the interlayer electrical and thermal
resistivity in a layered metal are calculated for Fermi liquid quasiparticles
which are scattered inelastically by two-dimensional antiferromagnetic spin
fluctuations. Both resistivities have a linear temperature dependence over a
broad temperature range. Extrapolations to zero temperature made from this
linear- range give values that appear to violate the Wiedemann-Franz law.
However, below a low-temperature scale, which becomes small close to the
critical point, a recovery of this law occurs. Our results describe recent
measurements on CeCoIn near a magnetic field-induced quantum phase
transition. Hence, the experiments do not necessarily imply a non-Fermi liquid
ground state.Comment: 4 pages, 2 figures; accepted to Phys. Rev. Let
Fermi surface of underdoped cuprate superconductors from interlayer magnetoresistance: closed pockets versus open arcs
An outstanding question about the underdoped cuprates concerns the true nature of their Fermi surface which appears as a set of disconnected arcs. Theoretical models have proposed two distinct possibilities: (1) each arc is the observable part of a partially hidden closed pocket and (2) each arc is open, truncated at its apparent ends. We show that measurements of the variation in the interlayer resistance with the direction of a magnetic field parallel to the layers can qualitatively distinguish closed pockets from open arcs. This is possible because the field can be oriented such that all electrons on arcs encounter a large Lorentz force and resulting magnetoresistance whereas some electrons on pockets escape the effect by moving parallel to the field. © 2010 The American Physical Society
Soybean Marketing Methods and Characteristics of Arkansas Grain Handlers
Arkansas producers should acquaint themselves with all marketing methods available to them. Of particular importance is the pervasiveness of price risk within the current economic climate. This bulletin provides insights into the current structure of the grain marketing industry, soybean handler characteristics, and the availability and use of marketing alternatives in Arkansas. Arkansas soybean handlers were surveyed in 1998 to determine the marketing practices of both handlers and producers for the 1996 crop year. Particular emphasis was placed on the types of contracting methods offered by these handlers. Both facility size and corporate structure were found to play a significant role in determining the types of marketing contracts offered as well as the frequency of usage by producers
Reply to "Comment on 'Anisotropic scattering in angular-dependent magnetoresistance oscillations of quasi-two-dimensional and quasi-one-dimensional metals: Beyond the relaxation-time approximation'"
In reply to the Comment by Kennett regarding our article, we clarify the key points at which we disagree with Kennett's derivation of the interlayer magnetoconductivity in layered metals and argue that our original derivation of this quantity is valid. © 2010 The American Physical Society
Interlayer transverse magnetoresistance in the presence of an anisotropic pseudogap
The interlayer magnetoresistance of a quasi-two-dimensional layered metal with a d-wave pseudogap is calculated semiclassically. An expression for the interlayer resistivity as a function of the strength and direction of the magnetic field, the magnitude of the pseudogap, temperature, and scattering rate is obtained. We find that the pseudogap, by introducing low-energy nodal quasiparticle contours, smooths the dependence on field direction in a manner characteristic of its anisotropy. We thus propose that interlayer resistance measurements under a strong field of variable orientation can be used to fully characterize an anisotropic pseudogap. The general result is applied to the case of a magnetic field parallel to the conducting layers using a model band structure appropriate for overdoped Tâ„“2201
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