  We investigate phonon-induced spin and charge relaxation mediated by
spin-orbit and hyperfine interactions for a single electron confined within a
double quantum dot. A simple toy model incorporating both direct decay to the
ground state of the double dot and indirect decay via an intermediate excited
state yields an electron spin relaxation rate that varies non-monotonically
with the detuning between the dots. We confirm this model with experiments
performed on a GaAs double dot, demonstrating that the relaxation rate exhibits
the expected detuning dependence and can be electrically tuned over several
orders of magnitude. Our analysis suggests that spin-orbit mediated relaxation
via phonons serves as the dominant mechanism through which the double-dot
electron spin-flip rate varies with detuning.
