In-plane field magnetoresistivity of Si two-dimensional electron gas in Si/SiGe quantum wells at 20 mK

We report measurements of in-plane field magnetoresistivity of the two-dimensional electrons in two Si/SiGe quantum wells with different disorder strength at 20 mK. For both samples, the ratio of the saturation resistivity in the high magnetic field to the zero-field resistivity was approximately constant in the high-density limit. In the metallic to insulating transition (MIT) regime, it is strongly enhanced and appears diverging as the electron density approaches a sample-dependent characteristic density $n^{\ast }$. $n^{\ast }$ is below $n_c$, the critical density of MIT at which the temperature dependence of resistivity changes sign. Disorder is believed to play an important role in this phenomenon. Furthermore, the field at which the magnetoresistivity saturates appears to extrapolate to zero, suggesting that ferromagnetic instability does not occur in Si/SiGe, at least down to $n\sim 0.3\times {10}^{11}/{\text{cm}}^2$.

Figure 1

(a) Magnetoresistivity of sample A at $T=20\text{mK}$. From top to bottom, the curves correspond to densities of 0.320, 0.325, 0.355, 0.346, 0.377, 0.437, 0.455, 0.500, 0.566, 0.619, 0.717, 0.769, and $1.15\times {10}^{11}/{\text{cm}}^2$. (b) Scaled magnetoresistivity $\rho \left(B_{\text{ip}}\right)/\rho \left(B_{\text{ip}}=0\right)$ as a function of $B_{\text{ip}}/B_s$.

Figure 2

(Color online) The ratio $R_{\text{ip}}\equiv \rho \left(B_{\text{ip}}>B_s\right)/\rho \left(B_{\text{ip}}=0\right)$ as a function of $n$ for (a) sample A and (b) sample B. The $n_c$ and $n^{\ast }$ are labeled by the arrows in each figure. (c) $R_{\text{ip}}$ plotted as a function of the scaled density $\left(n-n^{\ast }\right)/n^{\ast }$.

Figure 3

(Color online) $B_s$ vs $n$. Data of samples A and B and data from Refs. 8, 13 are shown on the same plot. The high-density linear fit is the dashed line. The power-law fit with an exponent of 1.3 is the gray dotted line.