We report the results of an experimental study of the magnetoresistance $\rho_{ xx}$ in two samples of $p$-Si/SiGe/Si with low carrier concentrations $p$=8.2$\times10^{ 10}$ cm$^{ -2}$ and $p$=2$\times10^{ 11}$ cm$^{ -2}$. The research was performed in the temperature range of 0.3-2 K in the magnetic fields of up to 18 T, parallel to the two-dimensional (2D) channel plane at two orientations of the in-plane magnetic field $B_{ \parallel}$ against the current $I$: $B_{ \parallel} \perp I$ and $B_{ \parallel} \parallel I$. In the sample with the lowest density in the magnetic field range of 0-7.2 T the temperature dependence of $\rho_{ xx}$ demonstrates the metallic characteristics ($d \rho_{ xx}/dT>$0). However, at $B_{ \parallel}$ =7.2 T the derivative $d \rho_{ xx}/dT$ reverses the sign. Moreover, the resistance depends on the current orientation with respect to the in-plane magnetic field. At $B_{ \parallel} \cong$ 13 T there is a transition from the dependence $\ln(\Delta\rho_{ xx} / \rho_{ 0})\propto B_{ \parallel}^2$ to the dependence $\ln(\Delta\rho_{ xx} / \rho_{ 0})\propto B_{ \parallel}$. The observed effects can be explained by the influence of the in-plane magnetic field on the orbital motion of the charge carriers in the quasi-2D system.
Categories: cond-mat.mes-hall