Antiferromagnetic order in multi-band Hubbard models for iron-pnictides

We investigate multi-band Hubbard models for the three iron 3$d$-$t_{2g}$ bands and the two iron 3$d$-$e_g$ bands in ${\rm La O Fe As}$ by means of the Gutzwiller variational theory. Our analysis of the paramagnetic ground state shows that neither Hartree--Fock mean-field theories nor effective spin models describe these systems adequately. In contrast to Hartree--Fock-type approaches, the Gutzwiller theory predicts that antiferromagnetic order requires substantial values of the local Hund's-rule exchange interaction. For the three-band model, the antiferromagnetic moment fits experimental data for a broad range of interaction parameters. However, for the more appropriate five-band model, the iron $e_g$ electrons polarize the $t_{2g}$ electrons and they substantially contribute to the ordered moment.Comment: 4 pages, 4 figure

Prediction of pressure-induced red shift of f->d(t2g) excitations in Cs2NaYCl6:Ce(3+) and its connection with bond length shortening

Quantum chemical calculations including embedding, scalar relativistic, and dynamic electron correlation effects on Cs2NaYCl6:(CeCl6)3- embedded clusters predict: (i) red shifts of the 4f->5d(t2g) transition with pressure and (ii) bond length shortening upon 4f->5d(t2g) excitation. Both effects are found to be connected which suggests that new high pressure spectroscopic experiments could reveal the sign of the bond length change.Comment: 6 pages text; 1 table; 3 figures; to be published in J.Chem.Phy

A New Phenomenology for the Disordered Mixed Phase

A universal phase diagram for type-II superconductors with weak point pinning disorder is proposed. In this phase diagram, two thermodynamic phase transitions generically separate a ``Bragg glass'' from the disordered liquid. Translational correlations in the intervening ``multi-domain glass'' phase are argued to exhibit a significant degree of short-range order. This phase diagram differs significantly from the currently accepted one but provides a more accurate description of experimental data on high and low-T$_c$ materials, simulations and current theoretical understanding.Comment: 15 pages including 2 postscript figures, minor changes in published versio

Genome engineering of woody plants : past, present and future

Engineered endonucleases that digest the specific sequences can be used to modify target genomes precisely. This is called “genome editing” and is used widely to modify the genome of various organisms. The DNA-binding domains of zinc finger (ZF) proteins were the first to be used as a genome editing tool, in the form of designed ZF nucleases and, more recently, transcription activator-like effector as well as the clustered, regularly interspaced, short palindromic repeats and CRISPR-associated protein 9 (CRISPR/Cas9) system that targets RNA–DNA rather than protein–DNA interactions have been used successfully. These are powerful tools with which targeted gene modifications can be introduced in various organisms, including various plant species. A key step in genome editing is the generation of a double-stranded DNA break that is specific to the target gene. This is achieved using custom-designed endonucleases, which enable site-directed mutagenesis via a non-homologous end joining repair pathway and/or gene targeting via homologous recombination to occur efficiently at specific sites in the genome. This review provides an overview of the current status of genomics and genetic engineering of woody plants, and recent advances in genome editing technologies in plants as well as fungi. We also discuss how these strategies can provide insights into molecular breeding technology for woody plants

Evidence for a temperature-induced spin-state transition of Co3+ in La2-xSrxCoO4

We study the magnetic susceptibility of mixed-valent La2-xSrxCoO4 single crystals in the doping range of 0.5<= x <= 0.8 for temperatures up to 1000 K. The magnetism below room temperature is described by paramagnetic Co2+ in the high-spin state and by Co3+ in the non-magnetic low-spin state. Above room temperature, an increase in susceptibility compared to the behavior expected from Co2+ is seen, which we attribute to a spin-state transition of Co3+. The susceptibility is analyzed by comparison to full-multiplet calculations for the thermal population of the high- and intermediate-spin states of Co3+

Electrical Control of Dynamic Spin Splitting Induced by Exchange Interaction as Revealed by Time Resolved Kerr Rotation in a Degenerate Spin-Polarized Electron Gas

The manipulation of spin degree of freedom have been demonstrated in spin polarized electron plasma in a heterostructure by using exchange-interaction induced dynamic spin splitting rather than the Rashba and Dresselhaus types, as revealed by time resolved Kerr rotation. The measured spin splitting increases from 0.256meV to 0.559meV as the bias varies from -0.3V to -0.6V. Both the sign switch of Kerr signal and the phase reversal of Larmor precessions have been observed with biases, which all fit into the framework of exchange-interaction-induced spin splitting. The electrical control of it may provide a new effective scheme for manipulating spin-selected transport in spin FET-like devices.Comment: 8 pages, 3 figures ; added some discussion

Microscopic Model and Phase Diagrams of the Multiferroic Perovskite Manganites

Orthorhombically distorted perovskite manganites, RMnO3 with R being a trivalent rare-earth ion, exhibit a variety of magnetic and electric phases including multiferroic (i.e. concurrently magnetic and ferroelectric) phases and fascinating magnetoelectric phenomena. We theoretically study the phase diagram of RMnO3 by constructing a microscopic spin model, which includes not only the superexchange interaction but also the single-ion anisotropy (SIA) and the Dzyaloshinsky-Moriya interaction (DMI). Analysis of this model using the Monte-Carlo method reproduces the experimental phase diagrams as functions of the R-ion radius, which contain two different multiferroic states, i.e. the ab-plane spin cycloid with ferroelectric polarization P//a and the bc-plane spin cycloid with P//c. The orthorhombic lattice distortion or the second-neighbor spin exchanges enhanced by this distortion exquisitely controls the keen competition between these two phases through tuning the SIA and DMI energies. This leads to a lattice-distortion-induced reorientation of P from a to c in agreement with the experiments. We also discuss spin structures in the A-type antiferromagnetic state, those in the cycloidal spin states, origin and nature of the sinusoidal collinear spin state, and many other issues.Comment: 23 pages, 19 figures. Recalculated results after correcting errors in the assignment of Dzyaloshinsky-Moriya vector

Coulombic Energy Transfer and Triple Ionization in Clusters

Using neon and its dimer as a specific example, it is shown that excited Auger decay channels that are electronically stable in the isolated monomer can relax in a cluster by electron emission. The decay mechanism, leading to the formation of a tricationic cluster, is based on an efficient energy-transfer process from the excited, dicationic monomer to a neighbor. The decay is ultrafast and expected to be relevant to numerous physical phenomena involving core holes in clusters and other forms of spatially extended atomic and molecular matter.Comment: 5 pages, 1 figure, to be published in PR

Controlling orbital moment and spin orientation in CoO layers by strain

We have observed that CoO films grown on different substrates show dramatic differences in their magnetic properties. Using polarization dependent x-ray absorption spectroscopy at the Co L$_{2,3}$ edges, we revealed that the magnitude and orientation of the magnetic moments strongly depend on the strain in the films induced by the substrate. We presented a quantitative model to explain how strain together with the spin-orbit interaction determine the 3d orbital occupation, the magnetic anisotropy, as well as the spin and orbital contributions to the magnetic moments. Control over the sign and direction of the strain may therefore open new opportunities for applications in the field of exchange bias in multilayered magnetic films

Semiflexible Filamentous Composites

Inspired by the ubiquity of composite filamentous networks in nature we investigate models of biopolymer networks that consist of interconnected floppy and stiff filaments. Numerical simulations carried out in three dimensions allow us to explore the microscopic partitioning of stresses and strains between the stiff and floppy fractions c_s and c_f, and reveal a non-trivial relationship between the mechanical behavior and the relative fraction of stiff polymer: when there are few stiff polymers, non-percolated stiff ``inclusions`` are protected from large deformations by an encompassing floppy matrix, while at higher fractions of stiff material the stiff network is independently percolated and dominates the mechanical response.Comment: Phys. Rev. Lett, to appear (4 pages, 2 figures