6,352 research outputs found
Spin-Orbit Based Coherent Spin Ratchets
The concept of ratchets, driven asymmetric periodic structures giving rise to
directed particle flow, has recently been generalized to a quantum ratchet
mechanism for spin currents mediated through spin-orbit interaction. Here we
consider such systems in the coherent mesoscopic regime and generalize the
proposal of a minimal spin ratchet model based on a non-interacting clean
quantum wire with two transverse channels by including disorder and by
self-consistently treating the charge redistribution in the nonlinear
(adiabatic) ac-driving regime. Our Keldysh-Green function based quantum
transport simulations show that the spin ratchet mechanism is robust and
prevails for disordered, though non-diffusive, mesoscopic structures. Extending
the two-channel to the multi-channel case does not increase the net ratchet
spin current efficiency but, remarkably, yields a dc spin transmission
increasing linearly with channel number.Comment: 23 pages, 7 figures; to be published in Chemical Physic
Theory of spin current in chiral helimagnet
We give detailed description of the transport spin current in the chiral
helimagnet. Under the static magnetic field applied perpendicular to the
helical axis, the magnetic kink crystal (chiral soliton lattice) is formed.
Once the kink crystal begins to move under the Galilean boost, the spin-density
accumulation occurs inside each kink and there emerges periodic arrays of the
induced magnetic dipoles carrying the transport spin current. The coherent
motion of the kink crystal dynamically generates the spontaneous
demagnetization field. This mechanism is analogous to the
D\"{o}ring-Becker-Kittel mechanism of the domain wall motion in ferromagnets.
To describe the kink crystal motion, we took account of not only the tangential
-fluctuations but the longitudinal -fluctuations around the
helimagnetic configuration. Based on the collective coordinate method and the
Dirac's canonical formulation for the singular Lagrangian system, we derived
the closed formulae for the mass, spin current and induced magnetic dipole
moment accompanied with the kink crystal motion. To materialize the theoretical
model presented here, symmetry-adapted material synthesis would be required,
where the interplay of crystallographic and magnetic chirality plays a key role
there.Comment: 16 pages, 6 figures, to be published in Phys. Rev.
On the Model of Computation of Place/Transition Petri Nets
In the last few years, the semantics of Petri nets has been investigated in several different ways. Apart from the classical "token game", one can model the behaviour of Petri nets via non-sequential processes, via unfolding constructions, which provide formal relationships between nets and domains, and via algebraic models, which view Petri nets as essentially algebraic theories whose models are monoidal categories. In this paper we show that these three points of view can be reconciled. More precisely, we introduce the new notion of decorated processes of Petri nets and we show that they induce on nets the same semantics as that of unfolding. In addition, we prove that the decorated processes of a net N can be axiomatized as the arrows of a symmetric monoidal category which, therefore, provides the aforesaid unification
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