Longitudinal conductivity in Si/SiGe heterostructure at integer filling factors

We have investigated temperature dependence of the longitudinal conductivity σ xx at integer filling factors ν=i for Si/SiGe heterostructure in the quantum Hall effect regime. It is shown that for odd i, when the Fermi level EF is situated between the valley-split levels, Δσxx is determined by quantum corrections to conductivity caused by the electron-electron interaction: Δσxx(T)∼lnT. For even i, when EF is located between cyclotron-split levels or spin-split levels, σxx∼exp[−Δi/T] for i=6,10, 12 and ∼exp[−(T0i/T)]1/2 for i=4,8. For further decrease of T, all dependences σxx(T) tend to almost temperature-independent residual conductivity σi(0). A possible mechanism for σi(0) is discussed