Interplay between sheet resistance increase and magnetotransport properties in LaAlO${}_3$/SrTiO${}_3$

We find that the sheet resistance ($R_s$) of patterned samples of ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ with a length scale of several microns may increase significantly at low temperatures in connection with driving electrical currents and applying in-plane magnetic fields. As the samples are warmed up, $R_s$ recovers to its original value with accelerated recovery near $70\mathrm{K}$ and $160\mathrm{K}$. Concomitantly with the increase in $R_s$, the carrier density and the mobility decrease and magnetotransport properties which may be linked to magnetism are suppressed.

Figure 1

(a) $R_s$ as a function of time at 5 K in a pattern with $d=5\mu$m as an in-plane magnetic field is increased in steps. Inset: A sketch of a typical pattern. (b) $R_s$ as a function of time at 5 K in a similar pattern as the current is increased in steps with smaller steps near 1 $\mu$A as shown in the inset for more patterns (black squares) and different cooling cycles of the same pattern (blue triangles).

Figure 2

(a) $R_s$ as a function of time at 5 K in a similar pattern as an in-plane magnetic field is applied in the sample plane and is increased in steps, and for each field, the current is increased in steps [as in Fig. 1b]. (b) $R_s$ as a function of time for several similar patterns as the angle $\theta$ between a magnetic field of 8 T and the normal to the interface is increased in steps.

Figure 3

(a) Temperature dependence of the relative increase in $R_s$ induced by in-plane fields or currents. $R_s^i$ is the initial $R_s$ and $R_s^f$ is $R_s$ after the induced increase. (b) Temperature dependence of $R_s$ during cooling (triangles) and during warming after an $R_s$ increase at low temperatures (circles).

Figure 4

(a) HE resistance vs perpendicular magnetic field for different resistance steps at 2 K (see text). The arrow indicates the $R_s$ increase direction. (b) Sheet carrier density and mobility as a function of $R_s$ for the different resistance steps at 2 K.

Figure 5

(a) The nonlinear part of the HE resistance ($R_{xy}^{nl}$) as a function of $n_s$. Solid squares and solid circles represent different sets of $R_s$ increases using the same pattern ($d=5\mu$m). Inset: $R_{xy}^{nl}$ vs $n_s$ for two other patterns. (b) The magnetoresistance $\Delta$R/$R_s=\frac{R_s\left(H\right)-R_s(H=0)}{R_s(H=0)}$ at $\theta ={90}^{\circ }$ as a function of $n_s$. Symbols are as in panel (a). (c) The magnetoresistance at 2 K as a function of $\theta$ with a field of 8 T for the resistance steps as shown in Fig. 4a. The arrow indicates the $R_s$-increase direction.

Figure 6

(a) The HE resistance vs perpendicular magnetic field for three different patterns with $d=50\mu$m marked with different symbols at 2 K. The dashed lines are extrapolations of high-field HE. (b) The HE resistance as a function of $\theta$ with a field of 8 T for the three different patterns at 2 K. (c) The deviation of the HE resistance angular dependence from a $\cos \theta$ behavior, ${\Delta }_{\mathrm{HE}}=R_{xy}\left(\theta \right)-R_{xy}(\theta =0)\cos \theta$, as a function of the angle $\theta$. (d) The maximal value of ${\Delta }_{\mathrm{HE}}$, ${\Delta }_{\mathrm{HE}}^{\max }$, as a function of the nonlinear part of the HE resistance, $R_{xy}^{nl}$, in nine different patterns ($d=50\mu$m).