Locally enhanced conductivity due to the tetragonal domain structure in LaAlO$_{3}$/SrTiO$_{3}$ heterointerfaces

Abstract: The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO${3}$ and TiO${2}$-terminated SrTiO$_{3}$ (STO). Transport and other measurements in this system show a plethora of diverse physical phenomena. To better understand the interface conductivity, we used scanning superconducting quantum interference device microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed on thermal cycling above the STO cubic-to-tetragonal structural transition temperature, implying that the local conductivity is strongly modified by the STO tetragonal domain structure. The interplay between substrate domains and the interface provides an additional mechanism for understanding and controlling the behaviour of heterostructures.

Local Conductivity Enhancement in LAO/STO Heterointerfaces

The research elucidated in this paper focuses on the local conductivity phenomena observed at the interface of LaAlO3 (LAO) and SrTiO3 (STO) heterostructures, examined using scanning superconducting quantum interference device (SQUID) microscopy. This advanced probe offers insights into the localized magnetic fields generated by currents in these complex oxide systems. The study identifies that, at low temperatures, the current is localized into highly conductive paths within a less conductive matrix. These paths are aligned along the crystallographic axes and are sensitive to structural changes induced by temperature variations, notably around the STO's cubic to tetragonal transition temperature.

Noteworthy findings include that these conductive paths are reconfigured when samples are thermally cycled above 105 K, coinciding with the STO's structural phase transition. This behavior indicates that the conductivity is heavily influenced by the tetragonal domain structure of STO. The study proposes that these domain structures are key to understanding the conductivity mechanisms and can be leveraged to control electronic properties in heterostructures.

The implications of this research extend to the design and manipulation of electronic devices based on oxide interfaces. These phenomena present a new mechanism by which the electronic properties of heterostructures can be engineered through precise control over the domain structures with potential applications in novel electronic devices.

The research also probes the relationship between these structures and observed phenomena such as superconductivity and magnetism in LAO/STO heterostructures. It highlights the complex interplay between the local structure and transport properties, challenging previously held assumptions about uniform conductivity in these materials.

Future exploration could delve deeper into the microstructural factors that influence conductivity and the role of strain and cooling rates during sample preparation. Potential extensions of this work may include theoretical modeling of domain formation and dynamics to further understand how subtle structural changes can profoundly affect electronic properties. Additionally, the impact of enhanced local conductivity on global electronic properties and their dependence on external parameters like magnetic fields offers a fertile ground for further research.

In conclusion, this paper serves as a crucial junction in understanding the local conductive behaviors arising from LAO/STO interfaces. The observed phenomena provide valuable learning points for the broader field of oxide interface engineering, emphasizing the need for integrated approaches combining experimental and theoretical techniques to harness and manipulate the fascinating properties of complex oxides.