5,382 research outputs found
Stabilization of the high-spin state of Co in LaCoRhO
The rhodium doping in the LaCoRhO perovskite series
() has been studied by X-ray diffraction, electric transport and
magnetization measurements, complemented by electronic structure GGA+U
calculations in supercell for different concentration regimes. No charge
transfer between Co and Rh is evidenced. The diamagnetic ground
state of LaCoO, based on Co in low-spin (LS) state, is disturbed
even by a small doping of Rh. The driving force is the elastic energy connected
with incorporation of a large Rh cation into the matrix of small LS
Co cations, which is relaxed by formation of large Co in
high-spin (HS) state in the next-nearest sites to the inserted Rh atom. With
increasing temperature, the population of Co in HS state increases
through thermal excitation, and a saturated phase is obtained close to room
temperature, consisting of a nearest-neighbor correlation of small (LS
Co) and large (HS Co and LS Rh) cations in a kind of
double perovskite structure. The stabilizing role of elastic and electronic
energy contributions is demonstrated in supercell calculations for dilute Rh
concentration compared to other dopants with various trivalent ionic radius.Comment: 8 pages, 8 figure
Beyond the local approximation to exchange and correlation: the role of the Laplacian of the density in the energy density of Si
We model the exchange-correlation (XC) energy density of the Si crystal and
atom as calculated by variational Monte Carlo (VMC) methods with a gradient
analysis beyond the local density approximation (LDA). We find the Laplacian of
the density to be an excellent predictor of the discrepancy between VMC and LDA
energy densities in each system. A simple Laplacian-based correction to the LDA
energy density is developed by means of a least square fit to the VMC XC energy
density for the crystal, which fits the homogeneous electron gas and Si atom
without further effort.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
MUBs inequivalence and affine planes
There are fairly large families of unitarily inequivalent complete sets of
N+1 mutually unbiased bases (MUBs) in C^N for various prime powers N. The
number of such sets is not bounded above by any polynomial as a function of N.
While it is standard that there is a superficial similarity between complete
sets of MUBs and finite affine planes, there is an intimate relationship
between these large families and affine planes. This note briefly summarizes
"old" results that do not appear to be well-known concerning known families of
complete sets of MUBs and their associated planes.Comment: This is the version of this paper appearing in J. Mathematical
Physics 53, 032204 (2012) except for format changes due to the journal's
style policie
Polylithiated (OLi2) functionalized graphane as a potential hydrogen storage material
Hydrogen storage capacity, stability, bonding mechanism and the electronic
structure of polylithiated molecules (OLi2) functionalized graphane (CH) has
been studied by means of first principle density functional theory (DFT).
Molecular dynamics (MD) have confirmed the stability, while Bader charge
analysis describe the bonding mechanism of OLi2 with CH. The binding energy of
OLi2 on CH sheet has been found to be large enough to ensure its uniform
distribution without any clustering. It has been found that each OLi2 unit can
adsorb up to six H2 molecules resulting into a storage capacity of 12.90 wt%
with adsorption energies within the range of practical H2 storage application.Comment: 11 pages, 4 figures, 1 table, Phys. Chem. Chem. Phys. (submitted
Quantifying spin Hall angles from spin pumping: Experiments and Theory
Spin Hall effects intermix spin and charge currents even in nonmagnetic
materials and, therefore, ultimately may allow the use of spin transport
without the need for ferromagnets. We show how spin Hall effects can be
quantified by integrating permalloy/normal metal (N) bilayers into a coplanar
waveguide. A dc spin current in N can be generated by spin pumping in a
controllable way by ferromagnetic resonance. The transverse dc voltage detected
along the permalloy/N has contributions from both the anisotropic
magnetoresistance (AMR) and the spin Hall effect, which can be distinguished by
their symmetries. We developed a theory that accounts for both. In this way, we
determine the spin Hall angle quantitatively for Pt, Au and Mo. This approach
can readily be adapted to any conducting material with even very small spin
Hall angles.Comment: 4 pages, 4 figure
A hard metallic material: Osmium Diboride
We calculate the structural and electronic properties of OsB2 using density
functional theory with or without taking into account spin-orbit (SO)
interaction. Our results show that the bulk modulus with and without SO
interaction are 364 and 365 Gpa respectively, both are in good agreement with
experiment (365-395 Gpa). The evidence of covalent bonding of Os-B, which plays
an important role to form a hard material, is indicated both in charge density,
atoms in molecules analysis, and density of states analysis. The good
metallicity and hardness of OsB2 might suggest its potential application as
hard conductors.Comment: Figures improve
Identification of hydrogen bonds using quantum electrodynamics
A method for the identification of hydrogen bonds was investigated from the viewpoint of the stress tensor density proposed by Tachibana and following other works in this field. Hydrogen bonds are known to exhibit common features with ionic and covalent bonds. In quantum electrodynamics, the covalent bond has been demonstrated to display a spindle structure of the stress tensor density. Importantly, this spindle structure is also seen in the hydrogen bond, although the covalency is considerably weaker than in a typical covalent bond. Distinguishing it from the ionic bond is most imperative for the identification of the hydrogen bond. In the present study, the directionality of the hydrogen bond is investigated as the ionic bond is nearly isotropic, while the hydrogen bond exhibits the directionality. It was demonstrated that the hydrogen bond can be distinguished from the ionic bond using the angle dependence of the largest eigenvalue of the stress tensor density
Four-terminal resistance of an interacting quantum wire with weakly invasive contacts
We analyze the behavior of the four-terminal resistance, relative to the
two-terminal resistance of an interacting quantum wire with an impurity, taking
into account the invasiveness of the voltage probes. We consider a
one-dimensional Luttinger model of spinless fermions for the wire. We treat the
coupling to the voltage probes perturbatively, within the framework of
non-equilibrium Green function techniques. Our investigation unveils the
combined effect of impurities, electron-electron interactions and invasiveness
of the probes on the possible occurrence of negative resistance.Comment: 10 pages, 7 figure
Understanding the Clean Interface between Covalent Si and Ionic Al2O3
The atomic and electronic structures of the (001)-Si/(001)-gamma-Al2O3
heterointerface are investigated by first principles total energy calculations
combined with a newly developed "modified basin-hopping" method. It is found
that all interface Si atoms are fourfold coordinated due to the formation of
Si-O and unexpected covalent Si-Al bonds in the new abrupt interface model. And
the interface has perfect electronic properties in that the unpassivated
interface has a large LDA band gap and no gap levels. These results show that
it is possible to have clean semiconductor-oxide interfaces
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