  Spontaneous breaking of rotational symmetry and preferential orientation of
stripe phases in the quantum Hall regime has attracted considerable
experimental and theoretical effort over the last decade. We demonstrate
experimentally and theoretically that the direction of high and low resistance
of the two-dimensional (2D) hole gas in the quantum Hall regime can be
controlled by an external strain. Depending on the sign of the in-plane shear
strain, the Hartree-Fock energy of holes or electrons is minimized when the
charge density wave (CDW) is oriented along [110] or [1-10] directions. We
suggest that shear strains due to internal electric fields in the growth
direction are responsible for the observed orientation of CDW in pristine
electron and hole samples.
