7,135 research outputs found
Running of Fermion Observables in Non-Supersymmetric SO(10) Models
We investigate the complete renormalization group running of fermion
observables in two different realistic non-supersymmetric models based on the
gauge group with intermediate symmetry breaking for both
normal and inverted neutrino mass orderings. Contrary to results of previous
works, we find that the model with the more minimal Yukawa sector of the
Lagrangian fails to reproduce the measured values of observables at the
electroweak scale, whereas the model with the more extended Yukawa sector can
do so if the neutrino masses have normal ordering. The difficulty in finding
acceptable fits to measured data is a result of the added complexity from the
effect of an intermediate symmetry breaking as well as tension in the value of
the leptonic mixing angle .Comment: 15 pages, 3 figures, 4 tables. Final version published in JHE
Symmetry Breaking Constraints: Recent Results
Symmetry is an important problem in many combinatorial problems. One way of
dealing with symmetry is to add constraints that eliminate symmetric solutions.
We survey recent results in this area, focusing especially on two common and
useful cases: symmetry breaking constraints for row and column symmetry, and
symmetry breaking constraints for eliminating value symmetryComment: To appear in Proceedings of Twenty-Sixth Conference on Artificial
Intelligence (AAAI-12
Superlattice-induced ferroelectricity in charge-ordered LaSrFeO
Charge-order-driven ferroelectrics are an emerging class of functional
materials, distinct from conventional ferroelectrics, where electron-dominated
switching can occur at high frequency. Despite their promise, only a few
systems exhibiting this behavior have been experimentally realized thus far,
motivating the need for new materials. Here, we use density functional theory
to study the effect of artificial structuring on mixed-valence solid-solution
LaSrFeO (LSFO), a system well-studied experimentally. Our
calculations show that A-site cation (111)-layered LSFO exhibits a
ferroelectric charge-ordered phase in which inversion symmetry is broken by
changing the registry of the charge order with respect to the superlattice
layering. The phase is energetically degenerate with a ground-state
centrosymmetric phase, and the computed switching polarization is 39
C/cm, a significant value arising from electron transfer between Fe
ions. Our calculations reveal that artificial structuring of LSFO and other
mixed valence oxides with robust charge ordering in the solid solution phase
can lead to charge-order-induced ferroelectricity
Emergent odd-parity multipoles and magnetoelectric effects on a diamond structure: implication to 5 transition metal oxides OsO ( K, Rb, and Cs)
We report our theoretical predictions on the linear magnetoelectric (ME)
effects originating from odd-parity multipoles associated with spontaneous spin
and orbital ordering on a diamond structure. We derive a two-orbital model for
electrons in orbitals by including the effective spin-orbit coupling
which arises from the mixing between and orbitals. We show that
the model acquires a net antisymmetric spin-orbit coupling once staggered spin
and orbital orders occur spontaneously. The staggered orders are accompanied by
odd-parity multipoles: magnetic monopole, quadrupoles, and toroidal dipoles. We
classify the types of the odd-parity multipoles according to the symmetry of
the spin and orbital orders. Furthermore, by computing the ME tensor using the
linear response theory, we show that the staggered orders induce a variety of
the linear ME responses. We elaborate all possible ME responses for each
staggered order, which are useful to identify the order parameter and to detect
the odd-parity multipoles by measuring the ME effects. We also elucidate the
effect of lowering symmetry by a tetragonal distortion, which leads to richer
ME responses. The implications of our results are discussed for transition
metal oxides, OsO ( K, Rb, and Cs), in which the order parameters
are not fully identified.Comment: 11 pages, 2 figures, 3 table
Novel magnetic orderings in the kagome Kondo-lattice model
We consider the Kondo-lattice model on the kagome lattice and study its
weak-coupling instabilities at band filling fractions for which the Fermi
surface has singularities. These singularites include Dirac points, quadratic
Fermi points in contact with a flat band, and Van Hove saddle points. By
combining a controlled analytical approach with large-scale numerical
simulations, we demonstrate that the weak-coupling instabilities of the
Kondo-lattice model lead to exotic magnetic orderings. In particular, some of
these magnetic orderings produce a spontaneous quantum anomalous Hall state.Comment: 15 pages, 11 figure
Magnetic structure and orbital ordering in BaCoO3 from first-principles calculations
Ab initio calculations using the APW+lo method as implemented in the WIEN2k
code have been used to describe the electronic structure of the
quasi-one-dimensional system BaCoO3. Both, GGA and LDA+U approximations were
employed to study different orbital and magnetic orderings. GGA predicts a
metallic ground state whereas LDA+U calculations yield an insulating and
ferromagnetic ground state (in a low-spin state) with an alternating orbital
ordering along the Co-Co chains, consistent with the available experimental
data.Comment: 8 pages, 9 figure
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