Tunneling between Edge States in a Quantum Spin Hall System

We analyze a quantum spin Hall device with a point contact connecting two of its edges. The contact supports a net spin tunneling current that can be probed experimentally via a two-terminal resistance measurement. We find that the low-bias tunneling current and the differential conductance exhibit scaling with voltage and temperature that depend nonlinearly on the strength of the electron-electron interaction.

Figure 1

Geometry of the QSH point contact device studied in this Letter. The full (dotted) lines represent helical edge states in equilibrium with the left (right) contact.

Figure 2

The two graphs show the charge tunneling current $I_c$ as a function of the applied voltage $V$ for different values of $K$ and $T$. [The spin tunneling current $I_s$ that transfers spin between the edges is given by $I_s=(\hslash /2e)I_c$.]

Figure 3

The dc component of the charge tunneling current $I_{c,0}$ as a function of $V_0$ for different values of $K$ and $V_1$. [The dc component of the accompanying spin tunneling current $I_{s,0}$ is given by $I_{s,0}=(\hslash /2e)I_{c,0}$.]