Longitudinal conductivity in Si/SiGe heterostructure at integer filling factors

We have investigated temperature dependence of the longitudinal conductivity ${\sigma }_{\mathrm{xx}}$ at integer filling factors $\nu =i$ for Si/SiGe heterostructure in the quantum Hall effect regime. It is shown that for odd i, when the Fermi level $E_F$ is situated between the valley-split levels, $\Delta {\sigma }_{\mathrm{xx}}$ is determined by quantum corrections to conductivity caused by the electron-electron interaction: $\Delta {\sigma }_{\mathrm{xx}}\mathrm{}\left(T\right)\mathrm{}\sim \ln T.\mathrm{}$ For even i, when $E_F$ is located between cyclotron-split levels or spin-split levels, ${\sigma }_{\mathrm{xx}}\sim \exp [-{\Delta }_i/T]$ for $i=6,10,12\mathrm{}$ and $\sim \exp [-{(T}_{0i}/T){]}^{1/2}$ for $i=4,8.\mathrm{}$ For further decrease of T, all dependences ${\sigma }_{\mathrm{xx}}\mathrm{}\left(T\right)\mathrm{}$ tend to almost temperature-independent residual conductivity ${\sigma }_i\mathrm{}\left(0\right).$ A possible mechanism for ${\sigma }_i\mathrm{}\left(0\right)\mathrm{}$ is discussed.