Softening of Spin-Wave Stiffness near the Ferromagnetic Phase Transition in Diluted Magnetic Semiconductors

Employing the self-consistent Green's function approach, we studied the temperature dependence of the spin-wave stiffness in diluted magnetic semiconductors. Note that the Green's function approach includes the spatial and temperature fluctuations simultaneously which was not possible within conventional Weiss mean-field theory. It is rather interesting that we found the stiffness becomes dramatically softened as the critical temperature is approached, which seems to explain the mysterious sharp drop of magnetization curves in samples within diffusive regime.Comment: 4 pages, 1 figur

Length and temperature dependent crossover of charge transport across molecular junctions

We study the electronic transport in a molecular junction in which each site is coupled to a local phonon bath using the non-equilibrium Green's function method. We observe the length period of the oscillatory conductance in odd-numbered chains depends strongly on the applied bias, and the oscillatory behavior is smeared out for the bias voltage near the phonon energy. In addition, a crossover from tunneling to thermally activated hopping transport as the length of the molecule increases is found for the phonon-free case. In the presence of electron-phonon interaction, hopping transport is dominant and a transition from the thermally suppressed to assisted conduction is observed.Comment: 9 pages, 10 figure

Origin of Ferromagnetism in nitrogen embedded ZnO:N thin films

Nitrogen embedded ZnO:N films prepared by pulsed laser deposition exhibit significant ferromagnetism. The nitrogen ions contained in ZnO confirmed by Secondary Ion Microscopic Spectrum and Raman experiments and the embedded nitrogen ions can be regarded as defects. According to the experiment results, a mechanism is proposed based on one of the electrons in the completely filled d-orbits of Zn that compensates the dangling bonds of nitrogen ions and leads to a net spin of one half in the Zn orbits. These one half spins strongly correlate with localized electrons that are captured by defects to form ferromagnetism. Eventually, the magnetism of nitrogen embedded ZnO:N films could be described by a bound magnetic polaron model.Comment: 7 pages, 6 figure

Zero-temperature magnetism in the periodic Anderson model in the limit of large dimensions

We study the magnetism in the periodic Anderson model in the limit of large dimensions by mapping the lattice problem into an equivalent local impurity self-consistent model. Through a recently introduced algorithm based on the exact diagonalization of an effective cluster hamiltonian, we obtain solutions with and without magnetic order in the half-filled case. We find the exact AFM-PM phase boundary which is shown to be of $2^{nd}$ order and obeys $\frac{V^2}{U} \approx const.$ We calculate the local staggered moments and the density of states to gain insights on the behavior of the AFM state as it evolves from itinerant to a local-moment magnetic regimeComment: 9 pages + 9 figures, to appear in Phys. Rev. B, 1 Sept. 1995 issu

Ptenb Mediates Gastrulation Cell Movements via Cdc42/AKT1 in Zebrafish

Phosphatidylinositol 3-kinase (PI3 kinase) mediates gastrulation cell migration in zebrafish via its regulation of PIP2/PIP3 balance. Although PI3 kinase counter enzyme PTEN has also been reported to be essential for gastrulation, its role in zebrafish gastrulation has been controversial due to the lack of gastrulation defects in pten-null mutants. To clarify this issue, we knocked down a pten isoform, ptenb by using anti-sense morpholino oligos (MOs) in zebrafish embryos and found that ptenb MOs inhibit convergent extension by affecting cell motility and protrusion during gastrulation. The ptenb MO-induced convergence defect could be rescued by a PI3-kinase inhibitor, LY294002 and by overexpressing dominant negative Cdc42. Overexpression of human constitutively active akt1 showed similar convergent extension defects in zebrafish embryos. We also observed a clear enhancement of actin polymerization in ptenb morphants under cofocal microscopy and in actin polymerization assay. These results suggest that Ptenb by antagonizing PI3 kinase and its downstream Akt1 and Cdc42 to regulate actin polymerization that is critical for proper cell motility and migration control during gastrulation in zebrafish

Model investigation of high-temperature superconductor/colossal manganite interfaces

A heterostructure interface between a high-temperature superconductor and a colossal magnet shows unexpected magnetic properties from experimental measurements. Namely, the copper moments appear in the interfaces. Further evidence has proven that the charge transfer occurs between the interface. To understand how the odd magnetic copper moment is induced and how the charge transfer dominates the magnetic orders in the interface, we propose a theoretical model to simulate the interface. Our calculation results confirm that the odd copper moment only coexists with the ferromagnetic moment of the colossal magnet. We also demonstrate that charge transfer between interfaces significantly affects superconducting and ferromagnetic order

The correlation between superconductivity and ferromagnetism in superconductor-ferromagnet heterostructures

The correlation between superconductivity and ferromagnetism through a magnetic coupling at the interface between the heterostructure constructed by high temperature superconductor and ferromagnet layers was theoretically investigated. The investigation results represent a fact that the superconductor and the ferromagnet affect mutually and the increase of the magnetic coupling will simultaneously suppress the ferromagnetism and the superconductivity. The dominant mechanism of the result is owing to the carrier exchange between both layers determined by the magnetic coupling strength and each layer’s orbital energy. The increase in the number of carriers will enhance the superconductivity as well as the ferromagnetism but with too many of carriers in the ferromagnet, the ferromagnetism will be suppressed by over spin screening