${\mathbf{LaAlO}}_{\mathbf{3}}/{\mathbf{SrTiO}}_{\mathbf{3}}$ interfaces doped with rare-earth ions

Doping the ${\mathrm{LaAlO}}_3$ (LAO) side of the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface with 2% Tm or Lu does not significantly affect its electron transport. Also, at low temperatures, carrier mobility is steeply anticorrelated with carrier concentration for both doped and undoped interfaces. This relationship cannot be explained by ionized impurities alone but may be driven by positive charge in or on the LAO film.

Figure 1

Upper panel: The out-of-plane magnetoresistance of a typical Lu-doped LAO/STO interface is parabolic at low fields and linear at higher fields, similar to undoped LAO/STO. Lower panel: Plotting the magnetoresistance against mobility times magnetic field $\left(\mu \times B\right)$ instead of $B$ mostly collapses the magnetoresistance curves onto a single universal curve, implying that the magnetoresistance is orbital in nature and mostly due to a single carrier type.

Figure 2

The Hall resistance of a typical Lu-doped LAO/STO interface at 2 K (Tm-doped and undoped interfaces are very similar). Although its nonlinearity suggests multiple carrier types, magnetoresistance measurements suggest that conductivity is dominated by the high-mobility carriers.

Figure 3

At low temperatures, carrier mobility $\mu$ is steeply anticorrelated with carrier concentration $n$. This is true of both our doped and undoped LAO/STO as well as for undoped LAO/STO from other groups [11, 12, 33, 34, 35, 36, 37, 38, 39, 40, 41]. A rough power-law fit to our own data shows that $\mu \propto n^{-3}$.