Thermally activated recovery of electrical conductivity inLaAlO3/SrTiO3

Abstract

Patterned structures of LaAlO3/SrTiO3 that exhibit a decrease in their electrical conductivity below 30 K, recover their higher conductivity upon warming in a thermally activated process. Two dominant energy barriers E b are identified: E b1 = 0.224 ± 0.003 eV related to conductivity recovery near 70 K and E b2 = 0.44 ± 0.015 eV related to conductivity recovery near 160 K. We discuss possible linkage to structural defects such as dislocations and twin boundaries. PACS numbers:An attractive feature of the interface between the insulating oxides SrTiO 3 and LaAlO 3 (LAO/STO) [1,2] is the ability to tune its transport properties by gate voltage [3][4][5][6][7][8][9][10]. However, it appears that there are other mechanisms that yield effectively the same effect without gating, including similar correlations between sheet resistance, carrier density and mobility. In a recent report [11], we showed that LAO/STO patterns with current path width smaller than 10 microns may exhibit below 30 K a significant decrease in their electrical conductivity, in connection with driving a sufficiently large current through the sample and/or applying an in-plane magnetic field. The initial high conductivity is recoverable upon applying a warming cycle.Concomitantly with the field-and current-induced decrease in conductivity, the sheet carrier density (n s ) and mobility decrease, magnetotransport features linked to magnetism [12][13][14] are suppressed, and the nonuniformity of the sample increases. Namely, without applying a gate voltage, there are mechanisms that decrease conductivity. Furthermore, the mechanism also increases the nonuniformity of the conductivity, a feature that was directly observed with scanning probe microscopy [15,16].Here, we explore in detail the time and temperature dependence of the conductivity recovery as the sample is warmed up and show that it is well described by a thermally activated process. We extract two energy barriers: E b1 = 0.224 ± 0.003 eV for the conductivity recovery near 70 K and E b2 = 0.44 ± 0.015 eV for the conductivity recovery near 160 K. The conductivity exhibits a noticeable time dependence also above room temperature; however, it can not be correlated with a single thermally-activated process.The results not only provide an explanation for a puzzling behavior reported previously [17,18], they also provide quantitative details on what appears to be a lowtemperature charge trapping mechanism that reduces the carrier density and increases nonuniformity. Thus, they provide new insights regarding two of the main issues concerning the transport properties of the LAO/STO interface: the existence and nature of localized charge carriers [19][20][21], and the origins of interface nonuniformity [12,15,16]. The identified energy scales and length scales are instrumental in identifying the trapping sites which would enable better understanding and control of the transport properties of the LAO/STO interface. Based on the relevant length scale of the phenomenon, we suggest that the trapping site...

Limit of the electrostatic doping in two-dimensional electron gases of LaXO3(X = Al, Ti)/SrTiO3

“…The same de-trapping behaviour has also been reported in LaAlO 3 /SrTiO 3 30 at similar temperatures. The authors associated this behaviour to a thermally activated mechanism supported by exponential relaxations of conductivity near 70 K and 160 K. However, this behaviour should not be confused with the low-temperature logarithmic relaxations observed after a gate voltage step that we described in the present article.…”

Current-induced nonuniform enhancement of sheet resistance in Ar+ -irradiated SrTiO3

“…This phenomenon occurs below ~40 K in connection with driving an electrical current through the sample exceeding a certain threshold. The initial as-cooled Rs recovers upon warming, particularly around 70 and 160 K, similar to the behavior exhibited by LAO/STO system [18,19] . To probe the microscopic manifestation of the effect we have used a scanning 3 superconducting quantum interference device (SQUID) and observed spatial changes in magnetic flux pattern prior to and after the Rs increase.…”

Anisotropic electronic transport of the two-dimensional electron system in Al2O3/SrTiO3 heterostructures

“…Data for sample II (not shown) are very similar. At 300 K n tot amounts to about 4×10 13 cm -2 and drops down to ≈ 2.5 ×10 13 cm -2 for T ≤ 10 K. The Tdependence of n tot is typical for 2DES in STO based heterostructures [26] and is usually interpreted as a freeze-out of charge carriers [33,34]. The Hall mobility of n hi was calculated by µ = (R s (B = 0)×n hi ×e) -1 , where e is the elementary charge.…”