M. Shayegan
Dept.
Electrical Engineering,
Two-dimensional
(2D) electrons in AlAs quantum wells occupy multiple
conduction-band minima (or valleys) at the X point of the Brillouin zone. These
valleys have large effective mass (m*) and g-factor compared to the standard GaAs electrons, and are also highly anisotropic. The system
is rather unique in that, with proper choice of well width and by applying in situ symmetry-breaking strain in the
plane, one can control the occupation of different valleys, thus rendering a
system with tuneable m*, g-factor, Fermi contour anisotropy, and with single,
double, or triple valley degeneracy.
By adding a magnetic field, we obtain a system which allows us to explore very
rich physics ensuing from the valley and spin degrees of freedom in a strongly
interacting system. In this presentation, I will highlight our latest results in
this system, including the observation of a metal-insulator transition and an
unexpected dependence of m* on the spin and valley polarizations.