Observation of the Zero Hall Plateau in a Quantum Anomalous Hall Insulator

We report experimental investigations on the quantum phase transition between the two opposite Hall plateaus of a quantum anomalous Hall insulator. We observe a well-defined plateau with zero Hall conductivity over a range of magnetic field around coercivity when the magnetization reverses. The features of the zero Hall plateau are shown to be closely related to that of the quantum anomalous Hall effect, but its temperature evolution exhibits a significant difference from the network model for a conventional quantum Hall plateau transition. We propose that the chiral edge states residing at the magnetic domain boundaries, which are unique to a quantum anomalous Hall insulator, are responsible for the novel features of the zero Hall plateau.

Figure 1

(a) Schematic drawing of the transport device used in this study. (b) Gate voltage $V_g$ dependence of ${\rho }_{yx}$ (blue curve) and ${\rho }_{xx}$ (red curve) measured at $T=10\mathrm{mK}$ in a $B=12\mathrm{T}$. (c) and (d) Magnetic field dependence of ${\rho }_{yx}$ (blue curve) (c) and ${\rho }_{xx}$ (red curve) (d) measured at $T=50\mathrm{mK}$ and $V_g=-5V$.

Figure 2

Low field part of the hysteretic anomalous Hall curve (blue curve) (a) and butterfly-shaped magnetoresistance (red curve) (b) measured at $T=50\mathrm{mK}$ and $V_g=-5V$. (c) Magnetic field dependence of ${\sigma }_{xx}$ (red curve) and ${\sigma }_{xy}$ (blue curve), showing a minimum of ${\sigma }_{xx}\sim 0.03e^2/h$ and a Hall plateau with ${\sigma }_{xy}=0$ around $H_C=0.16\mathrm{T}$.

Figure 3

(a) to (g): The ${\sigma }_{xy}$ for various $V_g$ values at $-30$, $-10$, $-5\mathrm{V}$, 0, $+5$, $+10$, and $+30$, respectively. The zero Hall plateau clearly exists for $V_g$ between $-10$ and $+10\mathrm{V}$ and becomes weakened when the $V_g$ value is increased to $\pm 30\mathrm{V}$.

Figure 4

The ${\sigma }_{xx}$ (a) and ${\sigma }_{xy}$ (b) measured at seven different temperatures at $V_g=-5V$. (c) Close correlation between the temperature dependences of zero Hall plateau width and ${\rho }_{yx}$ value at 12 T. (d) Dependence of the peak ${\rho }_{xx}$ value at $H_C$ (black open squares) and the maximum slope of ${\sigma }_{xy}$ vs ${\mu }_{0}H$ curve near $H_C$ (blue open circles). The dashed red line shows the variable range hopping fit between 200 mK to and 3 K. Note both the $x$ and $y$ axes are in logarithmic scale.