Colossal Magnetoresistance in an Ultraclean Weakly Interacting 2D Fermi Liquid

We report the observation of a new phenomenon of colossal magnetoresistance in a 40 nm wide GaAs quantum well in the presence of an external magnetic field applied parallel to the high-mobility 2D electron layer. In a strong magnetic field, the magnetoresistance is observed to increase by a factor of $\sim 300$ from 0 to 45 T without the system undergoing any metal-insulator transition. We discuss how this colossal magnetoresistance effect cannot be attributed to the spin degree of freedom or localization physics, but most likely emanates from strong magneto-orbital coupling between the two-dimensional electron gas and the magnetic field. Our observation is consistent with a field-induced 2D-to-3D transition in the confined electronic system.

Figure 1

(a) Longitudinal resistance $R_{xx}$ as a function of the parallel magnetic field $B_{\parallel }$ at temperatures $T=0.18\mathrm{K}$ (solid red line), 0.55 K (dashed blue line), and 1.05 K (dotted purple line). The increase in resistivity $\rho (B_{\parallel })/\rho (0)$ is shown on the right-hand scale, where $\rho (0)$ is the $T=0.18\mathrm{K}$ zero-field resistivity. The black line shows the CMR effect at $T=20\mathrm{mK}$ measured in an ultrahigh mobility 30 nm wide quantum well, shown here plotted on the right-hand $y$ axis, for comparison. Inset: Increase in resistance for fields up to 45 T at $T=0.51\mathrm{K}$. The right-hand $y$ axis gives the value for the metallicity parameter $k_f\lambda$ estimated from $\rho (B_{\parallel })$. (b),(c) Expanded plot in the vicinity of the 8 and 12 T magnetic field regions.

Figure 2

(a) Longitudinal resistance $R_{xx}$ and (b) normalized resistivity versus temperature. The dotted lines are guides to the eye.

Figure 3

Comparison of the resistivity versus parallel field between a tilted 40 nm quantum well [20] at $\theta =68.35°$ (red line), $\theta =64.5°$ (blue line), and the pure parallel-field case studied in this work, $\theta =90°$ (black line). The inset shows the same data for the $\theta =68.35°$ tilt angle and $\theta =90°$ but on a semilog scale.