2,062 research outputs found
Theory of one and two donors in Silicon
We provide here a roadmap for modeling silicon nano-devices with one or two
group V donors (D). We discuss systems containing one or two electrons, that
is, D^0, D^-, D_2^+ and D_2^0 centers. The impact of different levels of
approximation is discussed. The most accurate instances -- for which we provide
quantitative results -- are within multivalley effective mass including the
central cell correction and a configuration interaction account of the
electron-electron correlations. We also derive insightful, yet less accurate,
analytical approximations and discuss their validity and limitations -- in
particular, for a donor pair, we discuss the single orbital LCAO method, the
Huckel approximation and the Hubbard model. Finally we discuss the connection
between these results and recent experiments on few dopant devices.Comment: 13 pages, 6 figure
Effect of strain on the orbital and magnetic ordering of manganite thin films and their interface with an insulator
We study the effect of uniform uniaxial strain on the ground state electronic
configuration of a thin film manganite. Our model Hamiltonian includes the
double-exchange, the Jahn-Teller electron-lattice coupling, and the
antiferromagnetic superexchange. The strain arises due to the lattice mismatch
between an insulating substrate and a manganite which produces a tetragonal
distortion. This is included in the model via a modification of the hopping
amplitude and the introduction of an energy splitting between the Mn e_g
levels. We analyze the bulk properties of half-doped manganites and the
electronic reconstruction at the interface between a ferromagnetic and metallic
manganite and the insulating substrate. The strain drives an orbital selection
modifying the electronic properties and the magnetic ordering of manganites and
their interfaces.Comment: 8 pages, 8 figure
Impact of the valley degree of freedom on the control of donor electrons near a Si/SiO_2 interface
We analyze the valley composition of one electron bound to a shallow donor
close to a Si/barrier interface as a function of an applied electric field. A
full six-valley effective mass model Hamiltonian is adopted. For low fields,
the electron ground state is essentially confined at the donor. At high fields
the ground state is such that the electron is drawn to the interface, leaving
the donor practically ionized. Valley splitting at the interface occurs due to
the valley-orbit coupling, V_vo^I = |V_vo^I| e^{i theta}. At intermediate
electric fields, close to a characteristic shuttling field, the electron states
may constitute hybridized states with valley compositions different from the
donor and the interface ground states. The full spectrum of energy levels shows
crossings and anti-crossings as the field varies. The degree of level
repulsion, thus the width of the anti-crossing gap, depends on the relative
valley compositions, which vary with |V_vo^I|, theta and the interface-donor
distance. We focus on the valley configurations of the states involved in the
donor-interface tunneling process, given by the anti-crossing of the three
lowest eigenstates. A sequence of two anti-crossings takes place and the
complex phase theta affects the symmetries of the eigenstates and level
anti-crossing gaps. We discuss the implications of our results on the practical
manipulation of donor electrons in Si nanostructures.Comment: 8 pages, including 5 figures. v2: Minor clarifying changes in the
text and figures. Change of title. As published in PR
Simplified Metrics Calculation for Soft Bit Detection in DVB-T2
The constellation rotation and cyclic quadrature component delay (RQD) technique has been adopted in the second generation terrestrial digital video broadcasting (DVB-T2) standard. It improves the system performance under severe propagation conditions, but introduces serious complexity problems in the hardware implementation of the detection process. In this paper, we present a simplified scheme that greatly reduces the complexity of the demapper by simplifying the soft bit metrics computation having a negligible overall system performance loss
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