Enhanced lattice polarization inSrTiO3/LaAlO3superlattices measured using optical second-harmonic generation

Abstract

Lattice polarization at the SrTiO 3 / LaAlO 3 interface was investigated by optical second harmonic generation. Superlattices with varying periodicity were employed to study the evolution of interface polarization, while separating substrate contributions. We observed large perpendicular optical nonlinearity, which abruptly increases when the sublattice thickness goes above 3 unit cells. The polarization is primarily in SrTiO 3 and develops up to 8 unit cells from the interface.

Impact of biaxial compressive strain on the heterostructures of paraelectrics KTaO3 and SrTiO3

“…Stronger biaxial compressive strain results in larger distortion. Similar FE-type distortions at STO-based n-type interfaces have been identified by many theoretical and experimental studies, for example, electron-doped LaAlO 3 /SrTiO 3 interfaces, [41][42][43][44] LaTiO 3 /SrTiO 3 interfaces. 45 Note that the atom relaxation direction at these n-type interfaces is reversed compared with p-type cases, i.e.…”

Control of electronic conduction at an oxide heterointerface using surface polar adsorbates

“…These data also suggest that many of the conflicting (and often contradictory) studies of this popular system can be explained by this observation, that is, whether measurements are made in situ 31 , or after various surface exposures (for example, atmospheric water, or solvent cleaning) [32][33][34] , the sensitive electronic structure of the interface may be dramatically altered. For example, the predicted electric field across the LaAlO 3 layer [18][19][20] was not observed in X-ray photoemission studies 32 that may be explained consistently because the surface adsorbates (in particular atmospheric water) induced by the ex-situ processing reduce V Uncom , or equally, the electrical field across the LaAlO 3 layer.…”

“…For example, the predicted electric field across the LaAlO 3 layer [18][19][20] was not observed in X-ray photoemission studies 32 that may be explained consistently because the surface adsorbates (in particular atmospheric water) induced by the ex-situ processing reduce V Uncom , or equally, the electrical field across the LaAlO 3 layer. In contrast, in the LaAlO 3 /SrTiO 3 superlattices of multiple interfaces, the interfaces relatively far away from the surface may not be significantly affected by adsorbates 34 .…”

Perovskite oxide heteroepitaxy

“…For the 1 and 2 unit cell layer samples, the measured SHG sample is equal to or smaller than the baseline of the intensity obtained from a bare STO substrate. In figure 2.8b, the data obtained from the superlattices is presented [69]. The SHG intensity increases almost linearly with the STO sublayer thickness n up to n = 8, after which it decreases.…”

“…Savoia et al measured the SHG signal of single n-type LAO/STO interfaces with different LAO thicknesses [68]. Ogawa et al measured the SHG intensity of LAO/STO superlattices (both n-and p-type interfaces) for different sublayer thicknesses [69]. Both papers ascribe the measured signal to the STO, in the case of Savoia to the polarizability of the free electrons at the interface and in the case of Ogawa to the lattice polarization of the STO.…”