1,945 research outputs found
Two Dimensional Spin-Polarized Electron Gas at the Oxide Interfaces
The formation of a novel spin-polarized 2D electron gas at the LaMnO
monolayer embedded in SrMnO is predicted from the first-principles
density-functional calculations. The La (d) electrons become confined in the
direction normal to the interface in the potential well of the La layer,
serving as a positively-charged layer of electron donors. These electrons
mediate a ferromagnetic alignment of the Mn t spins near the interface
via the Anderson-Hasegawa double exchange and become, in turn, spin-polarized
due to the internal magnetic fields of the Mn moments.Comment: 5 pages, 6 figure
Strain and Electric Field Modulation of the Electronic Structure of Bilayer Graphene
We study how the electronic structure of the bilayer graphene (BLG) is
changed by electric field and strain from {\it ab initio} density-functional
calculations using the LMTO and the LAPW methods. Both hexagonal and Bernal
stacked structures are considered. The BLG is a zero-gap semiconductor like the
isolated layer of graphene. We find that while strain alone does not produce a
gap in the BLG, an electric field does so in the Bernal structure but not in
the hexagonal structure. The topology of the bands leads to Dirac circles with
linear dispersion in the case of the hexagonally stacked BLG due to the
interpenetration of the Dirac cones, while for the Bernal stacking, the
dispersion is quadratic. The size of the Dirac circle increases with the
applied electric field, leading to an interesting way of controlling the Fermi
surface. The external electric field is screened due to polarization charges
between the layers, leading to a reduced size of the band gap and the Dirac
circle. The screening is substantial in both cases and diverges for the Bernal
structure for small fields as has been noted by earlier authors. As a biproduct
of this work, we present the tight-binding parameters for the free-standing
single layer graphene as obtained by fitting to the density-functional bands,
both with and without the slope constraint for the Dirac cone.Comment: 7 pages, 7 figure
Anatomy of neck configuration in fission decay
The anatomy of neck configuration in the fission decay of Uranium and Thorium
isotopes is investigated in a microscopic study using Relativistic mean field
theory. The study includes and in the valley of stability
and exotic neutron rich isotopes , , , ,
, likely to play important role in the r-process
nucleosynthesis in stellar evolution. Following the static fission path, the
neck configurations are generated and their composition in terms of the number
of neutrons and protons are obtained showing the progressive rise in the
neutron component with the increase of mass number. Strong correlation between
the neutron multiplicity in the fission decay and the number of neutrons in the
neck is seen. The maximum neutron-proton ratio is about 5 for U and
Th suggestive of the break down of liquid-drop picture and inhibition
of the fission decay in still heavier isotopes. Neck as precursor of a new mode
of fission decay like multi-fragmentation fission may also be inferred from
this study.Comment: 16 pages, 5 figures (Accepted
Electronic and Magnetic Structure of the (LaMnO)/(SrMnO) Superlattices
We study the magnetic structure of the (LaMnO)/(SrMnO)
superlattices from density-functional calculations. In agreement with the
experiments, we find that the magnetism changes with the layer thickness `n'.
The reason for the different magnetic structures is shown to be the varying
potential barrier across the interface, which controls the leakage of the
Mn-e electrons from the LMO side to the SMO side. This in turn affects the
interfacial magnetism via the carrier-mediated Zener double exchange. For n=1
superlattice, the Mn-e electrons are more or less spread over the entire
lattice, so that the magnetic behavior is similar to the equivalent alloy
compound LaSrMnO. For larger n, the e electron transfer
occurs mostly between the two layers adjacent to the interface, thus leaving
the magnetism unchanged and bulk-like away from the interface region.Comment: 5 pages, 5 figure
Effects of strain on orbital ordering and magnetism at perovskite oxide interfaces: LaMnO3/SrMnO3
We study how strain affects orbital ordering and magnetism at the interface between SrMnO3 and LaMnO3 from density-functional calculations and interpret the basic results in terms of a three-site Mn-O-Mn model. Magnetic interaction between the Mn atoms is governed by a competition between the antiferromagnetic superexchange of the Mnβt2g core spins and the ferromagnetic double exchange of the itinerant eg electrons. While the core electrons are relatively unaffected by the strain, the orbital character of the itinerant electron is strongly affected, which in turn causes a large change in the strength of the ferromagnetic double exchange. The epitaxial strain produces the tetragonal distortion of the MnO6 octahedron, splitting the Mnβeg states into x2βy2 and 3z2β1 states, with the former being lower in energy, if the strain is tensile in the plane and opposite if the strain is compressive. For the case of the tensile strain, the resulting higher occupancy of the x2βy2 orbital enhances the in-plane ferromagnetic double exchange owing to the larger electron hopping in the plane, causing at the same time a reduction in the out-of-plane double exchange. This reduction is large enough to be overcome by antiferromagnetic superexchange, which wins to produce a net antiferromagnetic interaction between the out-of-plane Mn atoms. For the case of the in-plane compressive strain, the reverse happens, viz., that the higher occupancy of the 3z2β1 orbital results in the out-of-plane ferromagnetic interaction, while the in-plane magnetic interaction remains antiferromagnetic. Concrete density-functional results are presented for the (LaMnO3)1/(SrMnO3)1 and (LaMnO3)1/ (SrMnO3)3 superlattices for various strain conditions.This work was supported by the U.S. Department of Energy under Grant No. DE-FG02-00ER45818
Polar catastrophe, electron leakage, and magnetic ordering at the LaMnO3/SrMnO3 interface
Electronic reconstruction at the polar interface LaMnO3/SrMnO3 (LMO/SMO) (100) resulting
from the polar catastrophe is studied from a model Hamiltonian that includes the double and super exchange interactions, the Madelung potential, and the Jahn-Teller coupling terms relevant for the manganites. We show that the polar catastrophe, originating from the alternately charged LMO layers and neutral SMO layers, is quenched by the accumulation of an extra half electron per cell in the interface region as in the case of the LaAlO3/SrTiO3 interface. In addition, the Mn eg electrons leak out from the LMO side to the SMO side, the extent of the leakage being controlled by the interfacial potential barrier and the substrate induced epitaxial strain. The leaked electrons
mediate a Zener double exchange, making the layers adjacent to the interface ferromagnetic, while the two bulk materials away from the interface retain their original type A or G antiferromagnetic structures. A half-metallic conduction band results at the interface, sandwiched by the two insulating bulks. We have also studied how the electron leakage and consequently the magnetic ordering are
affected by the substrate induced epitaxial strain. Comparisons are made with the results of the density-functional calculations for the (LMO)6/(SMO)4 superlattice.This work was supported by the U. S. Department of Energy through Grant No. DE-FG02-00ER45818
Electronic and magnetic structure of the (LaMnO3)2n/(SrMnO3)n superlattices
We study the magnetic structure of the (LaMnO3)2n/(SrMnO3)n superlattices from density-functional calculations. In agreement with the experiments, we find that the magnetism changes with the layer thickness n. The reason for the different magnetic structures is shown to be the varying potential barrier across the interface, which controls the leakage of the Mn-eg electrons from the LaMnO3 side to the SrMnO3 side. This in turn affects the interfacial magnetism via the carrier-mediated Zener double exchange. For the n=1 superlattice, the Mn-eg electrons are more or less spread over the entire lattice so that the magnetic behavior is similar to the equivalent alloy compound La2/3Sr1/3MnO3. For larger n, the eg electron transfer occurs mostly between the two layers adjacent to the interface, thus leaving the magnetism unchanged and bulklike away from the interface region.This work was supported by the U.S. Department of Energy under Grant No. DE-FG02-00ER45818. We thank J. W. Freeland for stimulating this work and for valuable discussions
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