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Register a new userCoupling lattice instabilities across the interface in ultrathin oxide heterostructures
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Oxide heterointerfaces constitute a rich platform for realizing novel functionalities in condensed matter. A key aspect is the strong link between structural and electronic properties, which can be modified by interfacing materials with distinct lattice symmetries. Here we determine the effect of the cubic-tetragonal distortion of $text{SrTiO}_3$ on the electronic properties of thin films of $text{SrIrO}_3$, a topological crystalline metal hosting a delicate interplay between spin-orbit coupling and electronic correlations. We demonstrate that below the transition temperature at 105 K, $text{SrIrO}_3$ orthorhombic domains couple directly to tetragonal domains in $text{SrTiO}_3$. This forces the in-phase rotational axis to lie in-plane and creates a binary domain structure in the $text{SrIrO}_3$ film. The close proximity to the metal-insulator transition in ultrathin $text{SrIrO}_3$ causes the individual domains to have strongly anisotropic transport properties, driven by a reduction of bandwidth along the in-phase axis. The strong structure-property relationships in perovskites make these compounds particularly suitable for static and dynamic coupling at interfaces, providing a promising route towards realizing novel functionalities in oxide heterostructures.
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The ferroelectric (FE) control of electronic transport is one of the emerging technologies in oxide heterostructures. Many previous studies in FE tunnel junctions (FTJs) exploited solely the differences in the electrostatic potential across the FTJs that are induced by changes in the FE polarization direction. Here, we show that in practice the junction current ratios between the two polarization states can be further enhanced by the electrostatic modification in the correlated electron oxide electrodes, and that FTJs with nanometer thin layers can effectively produce a considerably large electroresistance ratio at room temperature. To understand these surprising results, we employed an additional control parameter, which is related to the crossing of electronic and magnetic phase boundaries of the correlated electron oxide. The FE-induced phase modulation at the heterointerface ultimately results in an enhanced electroresistance effect. Our study highlights that the strong coupling between degrees of freedom across heterointerfaces could yield versatile and novel applications in oxide electronics.
Atomically flat interfaces between ternary oxides have chemically different variants, depending on the terminating lattice planes of both oxides. Electronic properties change with the interface termination which affects, for instance, charge accumulation and magnetic interactions at the interface. Well-defined terminations have yet rarely been achieved for oxides of ABO3 type (with metals A, B). Here, we report on a strategy of thin film growth and interface characterization applied to fabricate the La0.7Sr0.3MnO3-SrRuO3 interface with controlled termination. Ultra-strong antiferromagnetic coupling between the ferromagnets occurs at the MnO2-SrO interface, but not for the other termination, in agreement with density functional calculations. X-ray magnetic circular dichroism measurements reveal coupled reversal of Mn and Ru magnetic moments at the MnO2-SrO interface. Our results demonstrate termination control of magnetic coupling across a complex oxide interface and provide a pathway for theoretical and experimental explorations of novel electronic interface states with engineered magnetic properties.
Interface engineering is an extremely useful tool for systematically investigating materials and the various ways materials interact with each other. We describe different interface engineering strategies designed to reveal the origin of the electric and magnetic dead-layer at La0.67Sr0.33MnO3 interfaces. La0.67Sr0.33MnO3 is a key example of a strongly correlated peroskite oxide material in which a subtle balance of competing interactions gives rise to a ferromagnetic metallic groundstate. This balance, however, is easily disrupted at interfaces. We systematically vary the dopant profile, the disorder and the oxygen octahedra rotations at the interface to investigate which mechanism is responsible for the dead layer. We find that the magnetic dead layer can be completely eliminated by compositional interface engineering such that the polar discontinuity at the interface is removed. This, however, leaves the electrical dead-layer largely intact. We find that deformations in the oxygen octahedra network at the interface are the dominant cause for the electrical dead layer.
The transport and magnetic properties of correlated La{0.53}Sr{0.47}MnO{3} ultrathin films, grown epitaxially on SrTiO{3}, show a sharp cusp at the structural transition temperature of the substrate. Using a combination of experiment and theory we show that the cusp is a result of resonant coupling between the charge carriers in the film and a soft phonon mode in the SrTiO{3}, mediated through oxygen octahedra in the film. The amplitude of the mode diverges towards the transition temperature, and phonons are launched into the first few atomic layers of the film affecting its electronic state.
A microscopic model Hamiltonian for the ferroelectric field effect is introduced for the study of oxide heterostructures with ferroelectric components. The long-range Coulomb interaction is incorporated as an electrostatic potential, solved self-consistently together with the charge distribution. A generic double-exchange system is used as the conducting channel, epitaxially attached to the ferroelectric gate. The observed ferroelectric screening effect, namely the charge accumulation/depletion near the interface, is shown to drive interfacial phase transitions that give rise to robust magnetoelectric responses and bipolar resistive switching, in qualitative agreement with previous density functional theory calculations. The model can be easily adapted to other materials by modifying the Hamiltonian of the conducting channel, and it is useful in simulating ferroelectric field effect devices particularly those involving strongly correlated electronic components where ab-initio techniques are difficult to apply.
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