Linear magnetoresistance in HgTe quantum wells

We report magnetotransport measurements in a HgTe quantum well with an inverted band structure, which is expected to be a two-dimensional (2D) topological insulator. A small magnetic field perpendicular the 2D layer breaks the time-reversal symmetry and thereby suppresses the edge state transport. A linear magnetoresistance is observed in low magnetic fields when the chemical potential moves through the bulk gap. That magnetoresistance is well described by numerical calculations of the edge state magnetotransport in the presence of nonmagnetic disorder. With the magnetic field increasing, both the local and nonlocal resistances first sharply decrease and then increase again in disagreement with the existing theories.

Figure 1

(a) Longitudinal $R_{xx}$ ($I=1,4$; $V=2,3$) and Hall $R_{xy}$ ($I=1,4$; $V=3,5$) resistances as a function of the gate voltage at zero and different nonzero magnetic fields, with $T=4.2$ K. (b) Nonlocal $R_{\mathrm{NL}}$ ($I=1,2$; $V=3,5$) resistance as a function of the gate voltage at zero and different nonzero magnetic fields. The inset (b) shows the top view of the sample. The gate is shown by a rectangle.

Figure 2

Longitudinal resistance $R_{xx}$ as a function of the gate voltage and magnetic field, with $T=1.4$ K.

Figure 3

Local $R_{xx}$ and nonlocal $R_{\mathrm{NL}}=R_{I=2,6;V=3,5}$ resistances as a function of the magnetic field near the peak maximum (CNP), with $T=4.2$ K.

Figure 4

Relative magnetoconductivity for two values of the gate voltage $V_g$ and two temperatures: (a) $T=1.4$ K and (b) $T=4.2$ K. Dashed lines are the functions ${\sigma }_{xx}\left(B\right)/{\sigma }_{xx}\left(0\right)=-\alpha \left|B\right|$. (c) Parameter $\alpha \approx d[{\sigma }_{xx}\left(B\right)/{\sigma }_{xx}\left(0\right)]dB$ as a function of the gate voltage for two temperatures: $T=1.4$ K (large circles) and $T=4.2$ K (small circles).