52,956 research outputs found
Superconductivity mediated by the antiferromagnetic spin-wave in chalcogenide iron-base superconductors
The ground state of KFeSe and other iron-based
selenide superconductors are doped antiferromagnetic semiconductors. There are
well defined iron local moments whose energies are separated from those of
conduction electrons by a large band gap in these materials. We propose that
the low energy physics of this system is governed by a model Hamiltonian of
interacting electrons with on-site ferromagnetic exchange interactions and
inter-site superexchange interactions. We have derived the effective pairing
potential of electrons under the linear spin-wave approximation and shown that
the superconductivity can be driven by mediating coherent spin wave excitations
in these materials. Our work provides a natural account for the coexistence of
superconducting and antiferromagnetic long range orders observed by neutron
scattering and other experiments.Comment: 4 pages, 3 figure
Parallel processing architecture for computing inverse differential kinematic equations of the PUMA arm
In advanced robot control problems, on-line computation of inverse Jacobian solution is frequently required. Parallel processing architecture is an effective way to reduce computation time. A parallel processing architecture is developed for the inverse Jacobian (inverse differential kinematic equation) of the PUMA arm. The proposed pipeline/parallel algorithm can be inplemented on an IC chip using systolic linear arrays. This implementation requires 27 processing cells and 25 time units. Computation time is thus significantly reduced
Metallic behaviour of carrier-polarized C molecular layers: Experiment and Theory
Although C is a molecular crystal with a bandgap E of ~2.5 eV, we
show that E is strongly affected by injected charge. In sharp contrast to
the Coulomb blockade typical of quantum dots, E is {\it reduced} by the
Coulomb effects. The conductance of a thin C layer sandwiched between
metal (Al, Ag, Au, Mg and Pt) contacts is investigated. Excellent Ohmic
conductance is observed for Al electrodes protected with ultra-thin LiF layers.
First-principles calculations, Hubbard models etc., show that the energy gap of
C is dramatically reduced when electrons hop from C to
C.Comment: 4 PRL style pages, 2 figures. email: [email protected]
Molecular electronics exploiting sharp structure in the electrode density-of-states. Negative differential resistance and Resonant Tunneling in a poled molecular layer on Al/LiF electrodes
Density-functional calculations are used to clarify the role of an ultrathin
LiF layer on Al electrodes used in molecular electronics. The LiF layer creates
a sharp density of states (DOS), as in a scanning-tunneling microscope (STM)
tip. The sharp DOS, coupled with the DOS of the molecule leads to negative
differential resistance (NDR). Electron transfer between oriented molecules
occurs via resonant tunneling. The I-V characteristic for a thin-film of tris
(8-hydroxyquinoline)- aluminum (AlQ) molecules, oriented using electric-field
poling, and sandwiched between two Al/LiF electrodes is in excellent agreement
with theory. This molecular device presents a new paradigm for a convenient,
robust, inexpensive alternative to STM or mechanical break-junction structures.Comment: 5 pages, 3 figure
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