The longitudinal resistance R xx of the SrTiO 3 / LaAlO 3 interface with magnetic fields applied perpendicular to the interface has an antisymmetric term ͓namely, R xx ͑H͒ R xx ͑−H͔͒ which increases with decreasing temperature and increasing field. We argue that the origin of this phenomenon is a nonhomogeneous Hall effect with clear contribution of an extraordinary Hall effect, suggesting the presence of nonuniform field-induced magnetization.The quasi-two-dimensional electron gas ͑q2DEG͒ that forms at the interface between the two insulating oxides, SrTiO 3 ͑STO͒ and LaAlO 3 ͑LAO͒, has fascinated many researchers who have been trying to elucidate the properties of this system. 1-9 Nevertheless, some of the most basic properties of this material are still controversial. Thus, contrary to the apparent consensus concerning the superconducting ground state of this system below 300 mK which obeys the Kosterlitz-Thouless phase transition, 3,10 the existence and nature of the magnetism are still open questions. While there is a theoretical prediction for a magnetic order, 11 the experimental situation is more complicated where some groups reported hysteretic magnetoresistance ͑MR͒ which suggests ferromagnetic order 12 and other reported lack of hysteresis but unusual magnetoresistance behavior which they attributed to some kind of magnetic order. 13 Here, we present data showing that the MR of the LAO/ STO interface with magnetic fields applied perpendicular to the interface has an antisymmetric term which increases with decreasing temperature and increasing field. While the qualitative behavior is common to all the patterns we have studied, the magnitude and the sign of the phenomenon vary considerably even between neighboring segments of the same pattern. Based on field, temperature, and angular dependent measurements of the Hall effect ͑HE͒ and the MR, we argue that the likely source of this phenomenon is a nonhomogeneous HE with a clear contribution of a nonuniform extraordinary Hall effect ͑EHE͒. 14 This interpretation implies that the applied magnetic field induces nonuniform magnetization. The nonuniform field-induced magnetization may suggest that either the induced magnetization is extrinsic to the q2DEG or that other nonuniformity affects locally the electron gas magnetization. The induced magnetization is likely to be the source of the observed large positive and negative MRs when magnetic fields are applied perpendicular and parallel to the interface, respectively. The negative MR is in the form of sharp and narrow dips, indicating strong magnetic anisotropy.While we do not resolve the elusive issue of magnetism in LAO/STO interfaces, we present multiple pieces of evidence for nonuniform field-induced magnetization at low temperatures which provide central ingredients for elucidating the nature of the q2DEG. The evidence for sizable EHE which we use for detecting the magnetism is of importance by itself for exploring the transport mechanism in this system and in addition it opens the door for future spintr...

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...

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The longitudinal resistance Rxx of the SrTiO3/LaAlO3 interface with magnetic fields applied perpendicular to the interface has an antisymmetric term (namely, Rxx(H) = Rxx(−H)) which increases with decreasing temperature and increasing field. We argue that the origin of this phenomenon is a non-homogeneous Hall effect with clear contribution of an extraordinary Hall effect, suggesting the presence of non-uniform field-induced magnetization.