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(a) The SrTiO3 (STO) heterostructures with an amorphous LaAlO3 (a-LAO) film exhibit the existence of a critical thickness for metal-insulator transition: As the LAO thickness (da-LAO) exceeds the critical thickness, the interface turns from a state with a high to a low sheet resistance (Rs). Inset: Schematic illustration of the sample setup. (b) By applying a back-gate potential by the scheme 0 V, 50 V, 0 V, and −50 V (lower pane), the resistive switching (RS) is not detectable for thick (here 5 nm, lower data-set, top pane) or extremely thin (<1.5 nm, upper data-set, top pane) LAO films, but readily observable for intermediate thicknesses (here 2 nm, middle data-set, top pane). Note that data points are omitted during a non-zero applied potential as—for the samples shown—this induced artifacts originating from a small, but changing voltage-gradient between the aluminum wires used to probe the transport properties. All measurements shown are performed at room temperature.
(a) For the a-LAO/STO heterostructure with an a-LAO thickness of 2 nm, the sheet resistance (Rs) is changed by around 3 orders of magnitude as the back-gate potential is altered. (b) The resistive switching is inferred to be caused by a modulation of the carrier density (ns). The characteristic times obtained by an exponential fit (solid lines) after removal of the positive or negative back-gate potential are seen to be 11 min and 17 min, respectively, indicating that the resistive switching is characterized by a long memory effect. (c) The back-gate potential (Vg) is changed by the scheme 0 V, 100 V, 0 V, and −100 V with each bias applied for 15 min at room temperature.
The resistive switching (RS) of the STO heterostructures with a 2 nm a-LAO (black circles, left axis) or 3 u.c. c-LAO (red triangles, right axis) top film is readily turned off upon lowering the temperature below 270 K. The switching ability is displayed in terms of the relative switching defined as (Rs −100 V − Rs +100 V)/Rs +100 V with Rs ±100 being the sheet resistance obtained right after application of a back-gate potential of ± 100 V for 15 min.
The resistive switching abilities can be tuned by maturing the sample as exemplified by an a-LAO/STO heterostructure with a 1.8 nm a-LAO film stored for 55 days at 0.8 bar in a desiccator. The heterostructure turned gradually from showing no observable switching in the sheet resistance (Rs) initially (lower data-set, top pane) to showing a clear resistive switching at later times (upper data-set, top pane) when applying a back-gate potential (Vg, lower pane) at room temperature.
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