Correlated Lattice Instability and Emergent Charged Domain Walls at Oxide Heterointerfaces

Abstract

Charged domain walls provide possibilities in effectively manipulating electrons at nanoscales for developing next-generation electronic devices. Here, using the atom-resolved imaging and spectroscopy on LaAlO 3 /SrTiO 3 // NdGaO 3 heterostructures, the evolution of correlated lattice instability and charged domain walls is visualized crossing the conducting LaAlO 3 /SrTiO 3 heterointerface. When increasing the SrTiO 3 layer thickness to 20 unit cells and above, both LaAlO 3 and SrTiO 3 layers begin to exhibit measurable polar displacements to form a tail-to-tail charged domain wall at the LaAlO 3 /SrTiO 3 interface, resulting in the charged redistribution within the 2-nm-thick SrTiO 3 layer close to the LaAlO 3 /SrTiO 3 interface. The mobile charges in different heterostructures can be estimated by summing up Ti 3+ concentrations in the conducting channel, which is sandwiched by SrTiO 3 layers with interdiffusion and/or oxygen octahedral rotations. Those estimated mobile charges are quantitatively consistent with results from Hall measurements. The results not only shed light on complex oxide heterointerfaces, but also pave a new path to nanoscale charge engineering.

Revealing the Photocharge-Transfer Mechanism at Manganite-Buffered LaAlO3/SrTiO3 Interfaces by Giant Photoresponse

“…Moreover, La diffusion into STO forms the localized positive charge, which causes the local lattice distortion and potential fluctuations, resulting in Anderson localization on the transferred 2D electrons. Thus, the La-diffused STO region becomes an insulator in dark . The R – T curves of samples illuminated by light show an insulator-to-metal transition below 110 K, which is near to the phase transition of STO at 105 K. A phenomenon similar to this was observed at LAO/STO interfaces with the visible light where the LAO thickness was less than the critical thickness .…”

“…Thus, the La-diffused STO region becomes an insulator in dark. 32 The R−T curves of samples illuminated by light show an insulator-to-metal transition below 110 K, which is near to the phase transition of STO at 105 K. A phenomenon similar to this was observed at LAO/ STO interfaces with the visible light where the LAO thickness was less than the critical thickness. 27 Interestingly, light makes the LAO/LSMO/STO behave like a conductor at low temperatures by suppressing the dead layer effect.…”

Controlling Transport Properties of 2D Electron System Hosted by SrTiO3‐Based Bilayers

“…The decrease of lattice mismatch is able to reduce the defect density and thus result in the suppression of Anderson localization at the LaAlO 3 / SrTiO 3 interface. [34,38] Therefore, more charges may become delocalized in the strain-engineered bilayer 2DES. Second, the properties of SrTiO 3 layer are more controllable compared with the SrTiO 3 substrate utilizing the growth parameters, such as the growth temperature T G and growth pressure P O2 for the SrTiO 3 layer.…”

Capping-layer-mediated lattice mismatch and redox reaction in SrTiO3-based bilayers

“…For examples, the model of polar discontinuity was proposed [10], and then experimentally examined by the observation of the critical thicknesses of various crystalline capping layers [11][12][13][14]. The interfacial lattice deformations that are determined by the capping layer can result in an internal polar field, which can be tuned to induce or eliminate the 2DES [15][16][17][18][19]. The capping layer that contains elements with high oxygen affinity, such as Al and Ti, can trigger the interfacial redox reaction and leave the conducting oxygen-deficient SrTiO 3−δ [20,21].…”

“…More importantly, the conclusion drawn from the SrTiO 3 substrate cannot be simply applied to the SrTiO 3 layer without modifications. This is because numerous differences between the SrTiO 3 single crystal and epitaxial layer can be found regarding various physics properties, such as the crystal lattice [16,17], band/orbital structures [34,35], dielectric constants [36,37], and defect energy levels [26,38]. Also, compared to the 2DES that is restrained by the SrTiO 3 substrate, the bilayer 2DES can be fabricated in combination with other functional layers, as well as industry-friendly substrates, to expand the application potentials in thin-film devices [39,40].…”