Magnetoresistance of two-dimensional electrons in Si/SiGe quantum wells in in-plane magnet field at 20 mK

We have measured the magnetoresistance of two-dimensional electrons in two modulation-doped Si/SiGe quantum wells in an in-plane magnetic field at 20mK. It was found that the ratio of the saturation resistance in high in-plane magnetic field to the zero-magnetic-field resistance is dependent on the electron density. At high electron density, the ratio is approximately 1.8. As the electron density decreases and is close to the metal-insulator transition, the ratio is strongly enhanced and appears diverging at a sample dependent characteristic density. The field at which the magnetoresistance saturates as a function of density is linear at high density. It deviates from this linear dependence and appears to extrapolate to zero when the electron density is below $\sim $0.7x10$^{11}$/cm$^{2}$.