Polar asymmetry of La(1−δ)Al(1+δ)O3/SrTiO3 heterostructures probed by optical second harmonic generation

Abstract

By combining transport measurements and optical second harmonic generation, we have investigated heterostructures formed between crystalline thin films of LaAlO 3 , with varying stoichiometry and TiO 2-terminated SrTiO 3 (001) substrates. Optical second harmonic generation directly probes the polarity of these heterostructures, thus complementing the transport data. The stoichiometry and the growth temperature are found to be critical parameters for controlling both the interfacial conductivity and the heterostructure polarity. In agreement with the previous work, all of the samples display an insulator-to-metal transition in the Al-reach region, with the conductivity first increasing and then saturating at the highest Al/La ratios. The second harmonic signal also increases as a function of the Al/La ratio, but, at the highest growth temperature, it does not saturate. This unusual behavior is consistent with the formation of an ordered structure of defect dipoles in the LaAlO 3 film caused by the off-centering of excess Al atoms in agreement with the theory. V

Visualizing quantum phenomena at complex oxide interfaces: An atomic view from scanning transmission electron microscopy

“…In particular, our main focus is to show the indispensability of STEM for understanding the properties of complex oxide interfaces and what needs to be improved and developed in the future. We note other techniques including synchrotronbased x-ray spectroscopies [33][34][35][36][37] (such as x-ray absorptions, x-ray linear dichroism and x-ray magnetic circular dichroism) and nonlinear optics [38][39][40] (such as second harmonic generations) are also powerful tools to study complex oxide interfaces.…”

Second Harmonic Generation Response in Thermally reconstructed Multiferroic β′- Gd2(MoO4)3 Thin Films

“…5(b) . This process is determined by the , where z the direction perpendicular to the interface, is the induced second-order polarization response, , is electric field of the incident photon and χ is the susceptibility tensor 71 , 72 . It is clear then, that this behavior is observed in materials without inversion symmetry, non centrosymmetric, hence, since ferro and piezo electrics require broken inversion symmetry, is an excellent method to probe ferroelectric materials.…”

Optical Second Harmonic Generation on LaAlO3/SrTiO3 Interfaces: A Review

“…In Ref. [ 48 ], SHG has been deployed to study such interfaces, and the main result is shown in Figure 9 , where different batches of samples grown at different temperatures and with different chemical composition are compared. The signal of the samples grown at about 720 C is only slightly increasing in the Al-rich region of the diagram, while the other two groups show a much more pronounced increase.…”