435 research outputs found
Coherent Particle Transfer in an On-Demand Single-Electron Source
Coherent electron transfer from a localized state trapped in a quantum dot
into a ballistic conductor, taking place in on-demand electron sources, in
general may result in excitation of particle-hole pairs. We consider a simple
model for these effects, involving a resonance level with time-dependent
energy, and derive Floquet scattering matrix describing inelastic transitions
of particles in the Fermi sea. We find that, as the resonance level is driven
through the Fermi level, particle transfer may take place completely without
particle-hole excitations for certain driving protocols. In particular, such
noiseless transfer occurs when the level moves with constant rapidity, its
energy changing linearly with time. A detection scheme for studying the
coherence of particle transfer is proposed.Comment: 5 pages, 3 figures. Updated introduction, Fig. 1, and reference
Electronic structure of (LaNiO)/(LaAlO) heterostructures grown along [111]
The electronic structure of a LaNiO bilayer grown along the [111]
direction and confined between insulating layers of LaAlO is theoretically
investigated using a combination of first principle calculations and effective
multi-orbital lattice models. The LDA band structure is well reproduced by a
tight-binding model for the Ni- orbitals defined on the buckled honeycomb
lattice. We highlight peculiar properties of this model which include almost
flat bands as well as linear and quadratic band crossing points. The effect of
local correlations is discussed within the LDA scheme and within the
Hartree-Fock approximation for interacting multi-orbital lattice models. Over a
wide range of interaction parameters we find that a ferromagnetic phase is
energetically favored. We discuss the possibility of additional orbital order
which could stabilize a spontaneous Chern insulator with chiral edge modes or a
staggered orbital phase with a reconstruction of the
unit cell. By studying an interacting nickel-oxygen lattice model we find that
the stability of these orbitally ordered phases also depends on the value of
the charge-transfer energy. Controlling the charge-transfer energy might
therefore be an important step towards engineering exotic electronic phases in
certain classes of oxide heterostructures.Comment: 11 pages, 11 figure
Counterintuitive transitions in the multistate Landau-Zener problem with linear level crossings
We generalize the Brundobler-Elser hypothesis in the multistate Landau-Zener
problem to the case when instead of a state with the highest slope of the
diabatic energy level there is a band of states with an arbitrary number of
parallel levels having the same slope. We argue that the probabilities of
counterintuitive transitions among such states are exactly zero.Comment: 9 pages, 5 figure
Spin-Filtering Multiferroic-Semiconductor Heterojunctions
We report on the structural and electronic properties of the interface
between the multiferoic oxide YMnO and wide band-gap semiconductor GaN
studied with the Hubbard-corrected local spin density approximation (LSDA+U) to
density-functional theory (DFT). We find that the band offsets at the interface
between antiferromagnetically ordered YMnO and GaN are different for
spin-up and spin-down states. This behavior is due to the spin splitting of the
valence band induced by the interface. The energy barrier depends on the
relative orientation of the electric polarization with respect to the
polarization direction of the GaN substrate suggesting an opportunity to create
magnetic tunnel junctions in this materials system.Comment: 4 pages, 4 figure
Electron attachment to SF6 and lifetimes of SF6- negative ions
We study the process of low-energy electron capture by the SF6 molecule. Our
approach is based on the model of Gauyacq and Herzenberg [J. Phys. B 17, 1155
(1984)] in which the electron motion is coupled to the fully symmetric
vibrational mode through a weakly bound or virtual s state. By tuning the two
free parameters of the model, we achieve an accurate description of the
measured electron attachment cross section and good agreement with vibrational
excitation cross sections of the fully symmetric mode. An extension of the
model provides a limit on the characteristic time of intramolecular vibrational
relaxation in highly-excited SF6-. By evaluating the total vibrational spectrum
density of SF6-, we estimate the widths of the vibrational Feshbach resonances
of the long-lived negative ion. We also analyse the possible distribution of
the widths and its effect on the lifetime measurements, and investigate
nonexponential decay features in metastable SF6-.Comment: 22 pages, 10 figures, submitted to Phys. Rev.
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