Dominant Mobility Modulation by the Electric Field Effect at the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ Interface

Caviglia et al. [Nature (London) 456, 624 (2008)] have found that the superconducting ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface can be gate modulated. A central issue is to determine the principal effect of the applied electric field. Using magnetotransport studies of a gated structure, we find that the mobility variation is almost 5 times that of the sheet carrier density. Furthermore, superconductivity can be suppressed at both positive and negative gate bias. These results indicate that the relative disorder strength strongly increases across the superconductor-insulator transition.

Figure 1

(a) $R(T)$ from $T=300\mathrm{K}$ before biasing. (b) Low temperature $R(T)$ for various gate voltages. (c) Superconducting critical temperature $T_c$ versus gate voltage.

Figure 2

Antisymmetrized Hall resistance versus magnetic field, $R_{xy}(H)$ for various $V_g$ at $T=0.1\mathrm{K}$. Lines are guides to the eye. Inset: Capacitance versus voltage at $T=0.1\mathrm{K}$.

Figure 3

Sheet carrier density $n_{2d}$ and electron mobility ${\mu }_H$ versus $V_g$, at $T=0.1\mathrm{K}$ (squares) and $T=2\mathrm{K}$ (circles). Closed and open symbols refer to high field (8 T) and low (2 T) field values of the Hall coefficient, respectively. Heavy lines are carrier density changes estimated from the capacitance data using top ($n_{c1}$) and bottom ($n_{c2}$) areas. Other lines are guides to the eye.

Figure 4

Sheet resistance at $V_g=0\mathrm{V}$ and $T=2\mathrm{K}$ after applying an extremal voltage $V_e$. Sweep two was performed after resetting the system at $T=300\mathrm{K}$. Inset: Electron distribution calculations at three bias voltages.