Stimulating Oxide Heterostructures: A Review on Controlling SrTiO₃‐Based Heterointerfaces with External Stimuli

Abstract

Oxides are an exciting class of electronic materials which share key properties with conventional semiconductors, but also bring new intrinsic functionalities that are not used in most current electronics: superconductivity, ferro-, pyro-, and piezoelectricity, ferromagnetism, and multiferrocity. Among the large number of oxides, strontium titanate (SrTiO 3 , STO) has been the center of attention in numerous studies for more than half a century. STO both serves as a popular template for epitaxial growth of oxide thin films as well as by itself exhibiting an attractive palettes of properties, including Numerous of the greatest inventions in modern society, such as solar cells, display panels, and transistors, rely on a simple concept: An external stimulus is applied to a material and the response is then utilized. Oxides often exhibit a colorful palette of responses to external stimuli due to the close coupling between lattice, spin, orbital, and charge degrees of freedom. In particular, oxide heterostructures where oxide thin films are deposited on SrTiO 3 have proven to be a fertile playground for material scientists, and a vast amount of interesting theoretical and experimental studies showcase the wide tunabilities of these heterostructures when subjected to external stimuli. Here, the authors review how the properties of SrTiO 3 -based heterostructures can be changed by external stimuli using electric fields, magnetic fields, light, stress, particle bombardment, liquids, gases, and temperature. The application of a single stimulus or several stimuli combined often leads to unexpected changes in properties which can open up for designing new devices as well as expanding the boundaries of our understanding within fundamental science. Hall of Fame Article is a research scientist at the Technical University of Denmark, Department of Energy Conversion and Storage. He received his B.Sc. (2009) and M.Sc. (2012) in nanoscience from the University of Copenhagen, followed by his Ph.D. (2017) and postdoc (2018) from the Technical University of Denmark. His work is currently focused on the physics of oxide materials and oxide devices for information technology and energy harvesting, including oxide electronics, memristors, internet of things, and thermoelectricity. Felix Trier is a postdoctoral researcher at CNRS/Thales, University Paris-Saclay. He obtained his B.Sc. (2009) and M.Sc. (2012) in nanoscience from the University of Copenhagen. Then he earned his Ph.D. degree (2016) from the Technical University of Denmark. His current research is focused on fabrication and characterization of metallic oxide heterointerface devices for the study of the spin-charge interconversion in 2D Rashba systems. His work concerns the LaAlO 3 /SrTiO 3 heterointerface 2D metal and its electrostatic tunability.Nini Pryds is a Professor and head of the research section "Functional Oxides" at the Department of Energy Conversion and Storage, Technical University of Denmark (DTU), where he is leading a group of researchers working in the field...

On the emergence of conductivity at SrTiO3-based oxide interfaces – an in-situ study

“…The interfaces were fabricated using 5 × 5 × 0.5 mm 3 TiO 2 -terminated SrTiO 3 (001) single crystal substrates. Amorphous LaAlO 3 , amorphous LaSr 1/8 Mn 7/8 O 3 and crystalline γ-Al 2 O 3 layers were grown by PLD at an oxygen pressure of 2 × 10 −6 mbar at room temperature, consistent with previous studies 2,9,35 . The thin films were grown by PLD using a KrF laser (λ = 248 nm) with a repetition rate of 0.5 Hz, and a laser fluence of 2.5 mJ cm −2 .…”

Dynamics of the spatial separation of electrons and mobile oxygen vacancies in oxide heterostructures

“…While there are other studies [19,[21][22][23]31,33,41,50,[52][53][54] that report changes in the oxygen vacancy profile at SrTiO 3 -based heterointerfaces, the involved dynamics of ions in a complex energy landscape, with strong concentration gradients and intrinsic electric fields, has not been discussed in detail yet. Consequently, several questions remain unclear: What are the driving forces involved in the oxygen vacancy redistribution?…”

Current vortices and magnetic fields driven by moving polar twin boundaries in ferroelastic materials

“…Another common effect is that polarity is generated near domain walls via the flexoelectric effect 10,11 , e.g., in CaTiO 3 [12][13][14] . Besides the isolated domain walls, emerging functional properties have also been found near the interfaces between different oxides [15][16][17] or different orientations of the same oxide 18 . For instance, the two-dimensional electron gas at the interface between SrTiO 3 /LaAlO 3 based heterostructures has been verified to be responsible for the occurrence of the interfacial conductivity [19][20][21] and superconductivity 22,23 .…”