Cancellation of electron and hole contributions to the Hall effect in ultrathin Bi films grown on GaAs(110)

Magnetotransport measurements have been performed on ultrathin Bi films grown on GaAs(110). While large positive magnetoresistance is observed at low temperatures, the Hall resistance is found to be extremely small. This is explained by the cancellation of contributions of electrons and holes, which are estimated to have close density and mobility values. By analogy with graphene near the charge neutral point, magnetotransport properties are discussed in relation to the formation of Dirac cones.

Figure 1

Schematic view of the experimental setup. Gold electrodes were prepared on noncleaved surfaces in advance. The cleavage of a 0.35-mm-thick GaAs wafer, deposition of Bi films, and magnetotransport measurements were performed in situ under low-temperature and ultrahigh vacuum conditions.

Figure 2

Typical annealing behavior of $R_{\mathrm{sq}}$ of a 1.8-nm-thick Bi film at $B=0$. Films as-deposited show superconductivity below 4–5 K. The abrupt increase at 40–60 K is attributed to a structural phase transition from the amorphous to crystalline phase. The decrease near 300 K can be understood as a result of improvement of crystallinity.

Figure 3

Magnetic-field dependence of (a) $R_{\mathrm{sq}}$ and (b) $R_{\mathrm{H}}$ of F1 at 1.7 K. The magnetic field is perpendicular to the film except for the dash-dotted line (blue) representing the parallel-magnetic-field dependence of $R_{\mathrm{sq}}$. Solid lines are the experimental data. Dotted lines (green) are the fits using Eqs. (1) and (2). Dashed lines (red) are the fits based on Eq. (5).

Figure 4

Plots of $f_e, {\mu }_e$, and ${\mu }_h$ vs $n_{\mathrm{loc}}$ obtained using the puddle model. Squares, diamonds, triangles, and circles are for F1 (1.7 K), F2 (1.5 K), F3 (4.2 K), and F4 (2.7, 14, 19, 29, 44, 68, 100, 156 K), respectively. Filled (open) symbols in the lower panel represent ${\mu }_e$ (${\mu }_h$). The low-temperature resistance of F4 is reproducible after the thermal cycling to 156 K.