Figure 2: Structural distortions and FE-like symmetry breaking in LAO/STO heterostructures. | Nature Communications

Figure 2: Structural distortions and FE-like symmetry breaking in LAO/STO heterostructures.

From: Hidden lattice instabilities as origin of the conductive interface between insulating LaAlO3 and SrTiO3

Figure 2

(a) The c axis variations and uc-volume changes in LAO/STO. The SXRD results of the heterostructures with various LAO thicknesses8 and in metallic 5-uc LAO/STO (refs 10, 11) are incorporated for comparison (omitting the associated error bars for clarity of the figure presentation). Grey dotted (dotted–dashed) line, 3.905 (3.762) Å of bulk STO (pseudomorphic-strained LAO). (b) The atomic displacements corresponding to a. Positive sign directs to the LAO surface. See text for detail. Each point in a and b represents the averaging over 150 separate analyses and this rigorous approach ensures a structural-evaluation precision of ∼0.02 Å. The thus-estimated error bars in a and b, ±0.02 Å, are omitted for clarity. (c,d) The respective PPA-determined ɛzz and ɛxx strain maps of insulating 3-uc and conductive 4-uc LAO/STO, showing the strain characteristics basically along c and a axes. The c axis elongation of interfacial STO uc shows an abrupt onset on the interfacial metallicity, 4 uc in c. The ab-plane of LAO is clamped by that of STO in both insulating and metallic heterostructure (d). Each HAADF image for the strain mapping is the sum of three separate ones. Colour scale bar, ±5% of strain with reference to a STO area far from the interface (out of the displayed range, 16 nm × 4 nm). (e) The colour-coded filtered annular bright-field imaging of the characteristic anti-phase oxygen-cage rotation (guiding white cages) in 10-uc LAO/STO, revealed along [110] projection. Guiding grey frames, uc. Scale bars in c–e, 1 nm.

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