5,180 research outputs found
Theory of spin injection
Diffusive theory of spin injection is reviewed and a number of new results is
presented for the dc and ac regimes. They were derived by means of the
"gamma-technique" allowing to simplify the calculations by choosing the spin
injection coefficients through different interfaces as the basic variables. The
prospects for increasing spin injection by using resistive spin-selective
contacts are emphasized and spin non-conserving contacts are introduced.
Finding the basic parameters of a junction from the ac data is discussed.Comment: 4 pages, 2 column REVTeX, to be published in Proceedings of Intern.
Symposium on Mesoscopic Superconductivity and Spintronics (Atsugi, March
2002
Complex impedance of a spin injecting junction
Theory of the ac spin injection from a ferromagnetic electrode into a normal
conductor through a tunnel or Schottky contact is developed. Diffusion and
relaxation of non-equilibrium spins results in a frequency dependent complex
impedance controlled by the spin relaxation rates and the resistances involved.
Explicit expression for the impedance is presented. Experimental investigation
of the frequency dependence of the impedance should allow measuring spin
relaxation times in both conductors, their effective resistances, and also the
parameters of the contact controlling the spin injection.Comment: 3 pages, 2 column REVTeX, to appear in Appl. Phys. Let
Diffusion theory of spin injection through resistive contacts
Insertion of a resistive contact between a ferromagnetic metal and a
semiconductor microstructure is of critical importance for achieving efficient
spin injection into a semiconductor. However, the equations of the diffusion
theory are rather cumbersome for the junctions including such contacts. A
technique based on deriving a system of self-consistent equations for the
coefficients of spin injection, "gamma", through different contacts are
developed. These equations are concise when written in the proper notations.
Moreover, the resistance of a two-contact junction can be expressed in terms of
"gamma"'s of both contacts. This equation makes calculating the spin valve
effect straightforward, allows to find an explicit expression for the junction
resistance and to prove that its nonequilibrium part is positive. Relation of
these parameters to different phenomena like spin-e.m.f. and the junction
transients is established. Comparative effect of the Coulomb screening on
different parameters is clarified. It is also shown that the spin
non-conservation in a contact can have a dramatic effect on the non-equilibrium
resistance of the junction.Comment: 16 pages, 2 column REVTeX format, minor editorial changes, references
to recent papers added, to appear in Euro. Phys. Journal
Driven nonlinear dynamics of two coupled exchange-only qubits
Inspired by creation of a fast exchange-only qubit (Medford et al., Phys.
Rev. Lett., 111, 050501 (2013)), we develop a theory describing the nonlinear
dynamics of two such qubits that are capacitively coupled, when one of them is
driven resonantly at a frequency equal to its level splitting. We include
conditions of strong driving, where the Rabi frequency is a significant
fraction of the level splitting, and we consider situations where the splitting
for the second qubit may be the same or different than the first. We
demonstrate that coupling between qubits can be detected by reading the
response of the second qubit, even when the coupling between them is only of
about of their level splittings, and calculate entanglement between
qubits. Patterns of nonlinear dynamics of coupled qubits and their entanglement
are strongly dependent on the geometry of the system, and the specific
mechanism of inter-qubit coupling deeply influences dynamics of both qubits. In
particular, we describe the development of irregular dynamics in a two-qubit
system, explore approaches for inhibiting it, and demonstrate existence of an
optimal range of coupling strength maintaining stability during the operational
time.Comment: 11 pages, 6 figures; One additional figure with changes to the text
about the results. Additional references include
Super-Resolution of Positive Sources: the Discrete Setup
In single-molecule microscopy it is necessary to locate with high precision
point sources from noisy observations of the spectrum of the signal at
frequencies capped by , which is just about the frequency of natural
light. This paper rigorously establishes that this super-resolution problem can
be solved via linear programming in a stable manner. We prove that the quality
of the reconstruction crucially depends on the Rayleigh regularity of the
support of the signal; that is, on the maximum number of sources that can occur
within a square of side length about . The theoretical performance
guarantee is complemented with a converse result showing that our simple convex
program convex is nearly optimal. Finally, numerical experiments illustrate our
methods.Comment: 31 page, 7 figure
Rainwater Harvesting Potential for Domestic Water Supply in Edo State
In the face of increasing scarcity of water resources, there is a need for communities to undertake audits of their current rainwater harvesting potential as a practical and promising alternative solution for water shortage. Despite the importance of rainwater harvest in socio-economic development of communities, very little information exists in the literature concerning it. This paper is an attempt to bridge this gap by examining the techniques and materials used for rainwater harvest with a focus on the geographical spread of its use and an analysis to support its wide acceptance by considering a case study from Edo State. Investigations also relate to health implications of rainwater harvest and impact on food production. Also, examined are institutional arrangements and policies guiding water supply and distribution in the state as opposed to rainwater harvest. The total volume of water supplied by the rain (in gallons), and the volume of conserved were evaluated from hydro-meteorological data collection system and through a survey in different senatorial districts of the state. The results of the analysis show that majority of the people empty their tanks mid-way into the dry season, suggesting that the current volume of the tanks is not enough to sustain the people with water during the dry season period. New constructions of bigger tanks are therefore recommended, particularly for families who use harvested rainwater for cassava processing.Rainwater, Harvesting, Edo State, Stream, Tanks
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