Giant negative magnetoresistance in high-mobility two-dimensional electron systems

We report on a giant negative magnetoresistance in very high mobility GaAs/AlGaAs heterostructures and quantum wells. The effect is the strongest at $B\simeq 1$ kG, where the magnetoresistivity develops a minimum emerging at $T\lesssim 2$ K. Unlike the zero-field resistivity which saturates at $T\simeq 2$ K, the resistivity at this minimum continues to drop at an accelerated rate to much lower temperatures and becomes several times smaller than the zero-field resistivity. Unexpectedly, we also find that the effect is destroyed not only by increasing temperature but also by modest in-plane magnetic fields. The analysis shows that giant negative magnetoresistance cannot be explained by existing theories considering interaction-induced or disorder-induced corrections.

Figure 1

(a) $\rho \left(B\right)$ of sample A at $0.5\text{K}\le T\le 1.75\text{K}$, with a step $\Delta T=0.25$ K. (b) $\rho \left(B\right)$ of sample B at $0.4\text{K}\le T\le 1.6\text{K}$, $\Delta T=0.2$ K. (c) $\rho \left(B\right)$ of sample A at $2\text{K}\le T\le 6\text{K}$, $\Delta T=0.5$ K. Arrows mark the second-order maxima of phonon-induced resistance oscillations (see text).

Figure 2

(a) ${\rho }_0$ (open circles) and ${\rho }_{\min }$ (solid circles) vs $T$ in sample A. (b) ${\rho }_{\min }/{\rho }_0$ vs $T$ in sample A (circles) and in sample B (squares). The vertical line “separates” high- and low-temperature regimes in sample A.

Figure 3

(a) $\rho \left(B\right)$ of sample C at $T=0.3$ K at different tilt angles $\theta$ (as marked). (b) ${\rho }_{\min }/{\rho }_0$ vs $1/\cos \theta$ (circles). The solid curve is a guide to an eye.

Figure 4

(a) The solid curves represent $\rho \left(B\right)/{\rho }_0$ measured in sample A at $T$ from $0.5$ to $2.0$ K, as marked. The dashed curves are fits to the data, $\rho \left(B\right)/{\rho }_0=1-\beta B^2$, at $\left|B\right|\le 0.5$ kG. (b), (c) $\beta$ vs $T$. The solid lines are fits to the data (see text) and the dashed lines are ${\beta }_i^{\mathrm{sm}}$ calculated using Eq. (3).