Spin-induced anomalous magnetoresistance at the (100) surface of hydrogen-terminated diamond

We report magnetoresistance measurements of hydrogen-terminated (100)-oriented diamond surfaces wherein an ionic-liquid-gated field-effect-transistor technique was used to make hole carriers accumulate. Unexpectedly, the observed magnetoresistance is positive within the range of $2<T<10$ K and $-7<B<7$ T, in striking contrast to the negative magnetoresistance previously detected for similar devices with (111)-oriented diamond surfaces. Furthermore, we find that (1) the magnetoresistance is orders of magnitude larger than that of the classical orbital magnetoresistance; (2) the magnetoresistance is nearly independent of the direction of the applied magnetic field; and (3) for the in-plane field, the magnetoresistance ratio, defined as $\left[\rho \right(B)-\rho (0\left)\right]/\rho \left(0\right)$, follows a universal function of $B/T$. These results indicate that the spin degree of freedom of hole carriers plays an important role in the surface conductivity of hydrogen-terminated (100) diamond.

Figure 1

(a) Optical micrograph of the Hall bar and schematic diagram of the ionic-liquid-gated field-effect transistor on the hydrogen-terminated (100) diamond surface. (b), (c) Temperature dependences of the sheet resistance $\rho$ (b) and Hall mobility (c) for gate voltages of $V_g=-1.4, -1.6$, and $-1.8$ V.

Figure 2

Magnetic field ($B$) dependence of the magnetoresistance ratio $\left[\rho \right(B)-\rho (0\left)\right]/\rho \left(0\right)$ measured for $V_g=-1.4, -1.6$, and $-1.8$ V at $T=2.0$ K by applying a magnetic field parallel and perpendicular to the diamond surface.

Figure 3

(a) Magnetic field ($B$) dependence of the magnetoresistance ratio $\left[\rho \right(B)-\rho (0\left)\right]/\rho \left(0\right)$ measured for $V_g=-1.8$ V at different temperatures by applying a magnetic field parallel to the diamond surface. (b) Plots of $\left[\rho \right(B)-\rho (0\left)\right]/\rho \left(0\right)$ as a function of $B/T$.

Figure 4

(a) Magnetic field ($B$) dependence of the magnetoresistance ratio $\left[\rho \right(B)-\rho (0\left)\right]/\rho \left(0\right)$ measured for $V_g=-1.8$ V at different temperatures by applying a magnetic field perpendicular to the diamond surface. (b) Plots of $\left[\rho \right(B)-\rho (0\left)\right]/\rho \left(0\right)$ as a function of $B/T$. (c) Plots of $\left[\rho \right(B)-\rho (0\left)\right]/\rho \left(0\right)$ as a function of $B/T^{1.32}$.

Figure 5

(a) Magnetoconductivity ratio $\left[\sigma \right(B)-\sigma (0\left)\right]/\sigma \left(0\right)$ as a function of $B/T$. The magnetic field is parallel to the diamond surface. The data for different gate voltages and different temperatures collapse onto a single curve. (b) The data shown in (a) are plotted in the form of $\sigma \left(B\right)-\sigma \left(0\right)$ vs $B/T$.