Spin-orbit coupling and electron-phonon scattering - Fachbereich ...

Chapter 4
Conclusion
In this part of the thesis we have investigated the effect of Rashba spin-orbit coupling
on parabolically confined nanostructures for the example of quantum wires
and few-electron quantum dots. In these systems the orbital motion is strongly
restricted due to the confinement which leads to characteristic spectral properties.
Since the spin-orbit interaction couples spin and orbital degrees of freedom, the
question arises, how the confinement induced modification of the orbital motion
affects the spin state of electrons in the nanostructure. This is of special interest
in the context of spintronics, where the spin is envisioned as an extension of even
substitute of the electron charge in future electronic devices.
In chapter 2, we investigated the combined effect of geometric confinement,
spin-orbit coupling, and magnetic field in quantum wires. In this interplay, the calculated
one-electron spectral and spin properties show a rich variety of characteristics.
These properties are governed by a compound spin orbital-parity symmetry.
Without magnetic field this spin parity – which is a characteristic property of any
symmetrically confined quasi-1D system with Rashba effect – is shown to replace
the quantum number of spin. It is also responsible for the well-known degeneracy
at k = 0 in symmetrically confined systems with Rashba effect. A non-vanishing
magnetic field breaks the spin-parity symmetry, thus lifting the corresponding degeneracy
at k = 0. We show that this magnetic field induced energy splitting can
become much larger than the Zeeman splitting and should be experimentally accessible
by means of optical or transport measurements. In addition, hybridisation
effects of the spin density go along with the symmetry breaking.
The one-electron spectrum is shown to be very sensitive to weak magnetic
fields. Spin-orbit induced modifications of the subband structure of the quantum
wire are strongly altered when the magnetic length becomes comparable to
the confinement. In the context of spintronics, this might imply consequences for
spin-field-effect-transistor designs which depend on spin injection from ferromagnetic
contacts because of magnetic stray fields.
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