Using relativity to improve electronic devices:
Ways to enhance the Rashba effect
by
Ulf Ekenberg(KTH)
→
Europe/Stockholm
FB41 (AlbaNova)
FB41
AlbaNova
Description
There is a rapidly growing interest in spin-related phenomena in
solids. The prospects of combining magnetic properties with the well
developed semiconductor technology have lead to a new research field
called spintronics. The spin polarization of electrons has clear analogies
to the polarization of light. I will illustrate the function of photonic
components and their spintronic counterparts. One of the best known
spintronic devices, the Datta-Das spin transistor, was introduced as an
analog to the electro-optic modulator. It is based on the so called Rashba
effect which is essentially of relativistic origin. Here an electric field
produces a spin splitting of subbands in a quantum well which is a
convenient way to control a spintronic device. The efforts to implement
this transistor in practice have not yet been successful. Calculations
of properties of spintronic devices commonly utilize the Rashba model in
which the strength is simply given by a coefficient. We use a more
elaborate multiband envelope function approach and obtain effects that
would not occur in simpler models. In this talk I will demonstrate some
novel ways in which the Rashba splitting can be efficiently controlled.
In a wide modulation-doped n-type quantum well one can utilize the
strong built-in electric field at the interfaces but turn on the Rashba
effect with a much smaller applied field.
In particular I show that with careful design one can increase the
wave-vector splitting relevant for the Datta-Das spin transistor by
several orders of magnitude by using holes instead of electrons. We
demonstrate how this superefficient Rashba effect can be investigated
experimentally. The implications for spintronic devices, in particular
the Datta-Das spin transistor, are discussed. The possibility of using
holes in spintronics has so far often been discarded because a strong
spin-orbit coupling also leads to rapid spin relaxation. We argue that
one can get around this problem in hole systems. There is furthermore
recent evidence that spin relaxation times can be comparable for electrons
and holes.