5,948 research outputs found
Entanglement of two delocalised electrons
Several convenient formulae for the entanglement of two indistinguishable
delocalised spin-1/2 particles are introduced. This generalizes the standard
formula for concurrence, valid only in the limit of localised or
distinguishable particles. Several illustrative examples are given.Comment: 4 page
Non-adiabatically driven electron in quantum wire with spin-orbit interaction
An exact solution is derived for the wave function of an electron in a
semiconductor quantum wire with spin-orbit interaction and driven by external
time dependent harmonic confining potential. The formalism allows analytical
expressions for various quantities to be derived, such as spin and pseudo-spin
rotations, energy and occupation probabilities for excited states. It is
demonstrated how perfect spin and pseudo-spin flips can be achieved at high
frequencies of order \omega, the confining potential level spacing. By an
appropriately chosen driving term, spin manipulation can be exactly performed
far into the non-adiabatic regime. Implications for spin-polarised emission and
spin-dependent transport are also discussed.Comment: 11 pages, 3 figure
General Green's function formalism for transport calculations with spd-Hamiltonians and giant magnetoresistance in Co and Ni based magnetic multilayers
A novel, general Green's function technique for elastic spin-dependent
transport calculations is presented, which (i) scales linearly with system size
and (ii) allows straightforward application to general tight-binding
Hamiltonians (spd in the present work). The method is applied to studies of
conductance and giant magnetoresistance (GMR) of magnetic multilayers in CPP
(current perpendicular to planes) geometry in the limit of large coherence
length. The magnetic materials considered are Co and Ni, with various
non-magnetic materials from the 3d, 4d, and 5d transition metal series.
Realistic tight-binding models for them have been constructed with the use of
density functional calculations. We have identified three qualitatively
different cases which depend on whether or not the bands (densities of states)
of a non-magnetic metal (i) form an almost perfect match with one of spin
sub-bands of the magnetic metal (as in Cu/Co spin valves); (ii) have almost
pure sp character at the Fermi level (e.g. Ag); (iii) have almost pure d
character at the Fermi energy (e.g. Pd, Pt). The key parameters which give rise
to a large GMR ratio turn out to be (i) a strong spin polarization of the
magnetic metal, (ii) a large energy offset between the conduction band of the
non-magnetic metal and one of spin sub-bands of the magnetic metal, and (iii)
strong interband scattering in one of spin sub-bands of a magnetic metal. The
present results show that GMR oscillates with variation of the thickness of
either non-magnetic or magnetic layers, as observed experimentally.Comment: 22 pages, 9 figure
Crystallization of the glassy phase of grain boundaries in silicon nitride
Three types of hot-pressed silicon nitride specimens (containing 5wt% Y2O3 and 2wt% Al2O3 additives) which were subjected to different temperature heat treatments were studied by X-ray diffraction, X-ray microanalysis and high resolution electron microscopy. The results indicated that there were phase changes in the grain boundaries after heat treatment and the glassy phase at the grain boundaries was crystallized by heat treatment
Spin detection at elevated temperatures using a driven double quantum dot
We consider a double quantum dot in the Pauli blockade regime interacting
with a nearby single spin. We show that under microwave irradiation the average
electron occupations of the dots exhibit resonances that are sensitive to the
state of the nearby spin. The system thus acts as a spin meter for the nearby
spin. We investigate the conditions for a non-demolition read-out of the spin
and find that the meter works at temperatures comparable to the dot charging
energy and sensitivity is mainly limited by the intradot spin relaxation.Comment: 8 pages, 6 figure
Entanglement between static and flying qubits in a semiconducting carbon nanotube
Entanglement can be generated by two electrons in a spin-zero state on a
semiconducting single-walled carbon nanotube. The two electrons, one weakly
bound in a shallow well in the conduction band, and the other injected into the
conduction band, are coupled by the Coulomb interaction. Both transmission and
entanglement are dependent on the well characteristics, which can be controlled
by a local gate, and on the kinetic energy of the injected electron. Regimes
with different degrees of electron correlation exhibit full or partial
entanglement. In the latter case, the maximum entanglement can be estimated as
a function of width and separation of a pair of singlet-triplet resonances.Comment: 17 pages and 12 figures, accepted to J. Phys. Cond. Ma
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