Light polarization and electron’s
spin angular momentum are very
intimately connected. One can easily
create left circularly polarized (LCP)
or right circularly polarized (RCP)
using a special kind of filter called
a circular polarizer (the same all
photographers use to eliminate
reflections from the surface of the
water for example). When RCP light (or
an RCP laser) is incident on a
semiconductor, only electrons of one
spin interact with that light. When
the light interacts with the electrons
it can give the electrons enough
energy to free them from the valence
shells of their parent atom. Free from
the valence shells, but still in the
material, these electrons are called free
because they have basically complete
mobility if exposed to an electric
field, and can form a spin -polarized
electric current.
Conversely, we can use light to detect
spin populations in semi conductors.
Light composed of half LCP and half
RCP is said to be linearly polarized
and we can assign a specific spatial
orientation to this polarization. When
lightbounces off a material with a net
spin population, the polarization of
the light changes by an angle directly
proportional to the spin population in
the material, in physics jargon this
is called the Kerr Effect. This effect
allows us to detect and map out the
regions of different spin population.
These Pictures took advantage of both
of these Phenomena to collect data.
What you see are the results of a
laser beam focused down to a 10 micron
beam diameter onto a Gallium Arsenide
thin film. The bands of color
represent different amounts of spin
polarization (detected by the Kerr
effect) in the excited electrons as
they drift under the bias of an
electric field.
(Each image above is 90 by 180 microns
in size)
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