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Sketch of the fabrication process: (a) deposition of PMMA and Cu layers, (b) e-beam exposure, (c) development of PMMA (after the Cu wet etch), (d) deposition of amorphous STO and (e) lift off, (f) deposition of the LAO film. In panel (g), an optical microscope image of one of the devices is shown before the amorphous STO lift-off procedure (full scale: 1.5 mm 1.2 mm). Panel (h) shows an atomic force microscope image of the bridge area. Polycrystalline/amorphous LAO, grown on the amorphous STO, has a lighter color, while the epitaxial LAO has a darker one. The 2DEG is created only below the epitaxial LAO.
Transport properties of the mesoscopic devices. Panel (a) shows typical curves of 500 nm (green line) and 800 nm (blue circles) bridges and of a large area ( ) (orange squares). Panel (b) displays the relative magnetoresistance, measured at 1.5 K, for the same three devices. The magnetic field was applied perpendicular to the sample. The solid red line is an example of the quadratic fit used to extract the carrier mobilities.
Transport parameters measured at 1.5 K of bridges of different width (blue circles) and of the adjoining large areas (orange squares): sheet resistance (a), mobility (b) and number of carriers (c). The green diamonds in panel (c) are the number of carriers estimated using the formula with and from panels (a) and (b).
Low temperature characterization of the mesoscopic bridges. Panels (a) and (b) show the gate modulation of the V–I characteristics for the 500 nm and 800 nm wide devices, respectively. Panel (c) shows magnetoconductance fluctuations measured for the 500 nm bridge. The conduction state was set using field effect. The two traces refer to opposite directions of the field sweep. All the measurements presented in this figure were carried out at 40 mK.
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