Single-edge transport in an InAs/GaSb quantum spin Hall insulator

We report transport measurements in a single edge channel of an InAs/GaSb quantum spin Hall insulator, where the conduction occurs through only one pair of counterpropagating edge modes. By using a specific sample design involving highly asymmetric current paths, we electrically isolate a single edge channel of the two-dimensional topological insulator from the other edge. This enables us to probe a single edge by multiterminal measurements. Both two-terminal and four-terminal resistances show a nearly quantized plateau around $h/e^2$ for a 4-$\mu \mathrm{m}$-long edge, indicating quasiballistic transport. Our approach is advantageous in that it allows us to gain insight into a microscopic region from local measurements.

Figure 1

(a) Schematic representation of the sample design. The close-up represents the main part of the device probed by transport measurements. (b) Schematics of band-edge profile of the heterostructure along the growth direction. (c) Illustration of the energy band diagram for inverted InAs/GaSb heterostructures. $\mathrm{\Delta }$ is the hybridization gap and $E_{g0}$ is the degree of band overlap.

Figure 2

(a) Schematic representation of the measurement configuration for the two-terminal resistance $R_{28,28}$ used to probe the bulk conduction. (b) Back-gate voltage $\left(V_{\text{BG}}\right)$ dependence of $R_{28,28}$ at different fixed front-gate voltage $V_{\text{FG}}$.

Figure 3

(a) Back-gate voltage dependence of the four-terminal resistance $R_{25,34}$ at different $V_{\text{FG}}$. (b) Evolution of the corresponding resistance peak amplitude at the CNP as a function of $V_{\text{FG}}$. In both (a) and (b), the horizontal dashed lines represent $h/e^2$.

Figure 4

Comparison of four-terminal resistances (a) $R_{25,87}$ and (b) $R_{25,34}$ as a function of $V_{\text{BG}}$ measured at $V_{\text{FG}}=-1$ V and at different temperatures. The vertical dashed lines in (a) demarcate the regime where the bulk conduction is suppressed at low temperature. The horizontal dashed line in (b) indicates $h/e^2$. Inset in (a): schematic representation of the measurement configuration.

Figure 5

Back-gate voltage dependence of two-terminal resistance $R_{34,34}$ (red) and four-terminal resistance $R_{25,34}$ (blue) measured at $V_{\text{FG}}=-1$ V. The vertical dashed lines indicate the bulk insulating regime shown in Fig. 4. The inset shows the respective measurement configurations.