Electron-electron interaction at decreasing $k_Fl$
  The contribution of the electron-electron interaction to conductivity is analyzed step by step in gated GaAs/InGaAs/GaAs heterostructures with different starting disorder. We demonstrate that the diffusion theory works down to $k_F l\simeq 1.5-2$, where $k_F$ is the Fermi quasimomentum, $l$ is the mean free paths. It is shown that the e-e interaction gives smaller contribution to the conductivity than the interference independent of the starting disorder and its role rapidly decreases with $k_Fl$ decrease. 
G.M.Minkov, O.E.Rut, A.V.Germanenko, A.A.Sherstobitov, V.I.Shashkin,   O.I.Khrykin, and B.N.Zvonkov