  We study theoretically the spin-flip relaxation processes for a single
electron in a self-assembled InAs/GaAs quantum dot, using an 8-band kp theory
in the envelope function approximation. We show that the dominating channel of
spin relaxation is spin admixture induced by symmetry-breaking shear strain,
which can be mapped onto two effective spin-phonon terms in a conduction band
(effective mass) Hamiltonian that have a similar structure and interfere
constructively. Unlike the Dresselhaus coupling that dominates spin relaxation
in larger, unstrained dots, the shear strain contribution cannot be modeled by
a unique standard term in the Hamiltonian but rather relies on the actual
strain distribution in the quantum dot.
