Contrast between spin and valley degrees of freedom

We measure the renormalized effective mass (m*) of interacting two-dimensional electrons confined to an AlAs quantum well while we control their distribution between two spin and two valley subbands. We observe a marked contrast between the spin and valley degrees of freedom: When electrons occupy two spin subbands, m* strongly depends on the valley occupation but not vice versa. Combining our m* data with the measured spin and valley susceptibilities, we find that the renormalized effective Lande g factor strongly depends on valley occupation but the renormalized conduction-band deformation potential is nearly independent of the spin occupation.