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Register a new userSuppression of twinning and enhanced electronic anisotropy of SrIrO3 films
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The spin-orbit coupling and electron correlation in perovskite SrIrO3 (SIO) strongly favor new quantum states and make SIO very attractive for next generation quantum information technology. In addition, the small electronic band-width offers the possibility to manipulate anisotropic electronic transport by strain. However, twinned film growth of SIO often masks electronic anisotropy which could be very useful for device applications. We demonstrate that the twinning of SIO films on (001) oriented SrTiO3 (STO) substrates can be strongly reduced for thin films with thickness t less than 30 nm by using substrates displaying a TiO2-terminated surface with step-edge alignment parallel to the a- or b-axis direction of the substrate. This allows us to study electronic anisotropy of strained SIO films which hitherto has been reported only for bulk-like SIO. For films with t < 30 nm electronic anisotropy increases with increasing t and becomes even twice as large compared to nearly strain-free films grown on (110) DyScO3. The experiments demonstrate the high sensitivity of electronic transport towards structural distortion and the possibility to manipulate transport by substrate engineering.
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Iridate oxides display exotic physical properties that arise from the interplay between a large spin-orbit coupling and electron correlations. Here, we present a comprehensive study of the effects of hydrostatic pressure on the electronic transport properties of SrIrO3 (SIO), a system that has recently attracted a lot of attention as potential correlated Dirac semimetal. Our investigations on untwinned thin films of SIO reveal that the electrical resistivity of this material is intrinsically anisotropic and controlled by the orthorhombic distortion of the perovskite unit cell. These effects provide another evidence for the strong coupling between the electronic and lattice degrees of freedom in this class of compounds. Upon increasing pressure, a systematic increase of the transport anisotropies is observed. The anomalous pressure-induced changes of the resistivity cannot be accounted for by the pressure dependence of the density of the electron charge carriers, as inferred from Hall effect measurements. Moreover, pressure-induced rotations of the IrO6 octahedra likely occur within the distorted perovskite unit cell and affect electron mobility of this system.
Magneto-transport properties of SrIrO$_3$ thin films epitaxially grown on SrTiO$_3$, using reactive RF sputtering, are investigated. A large anisotropy between the in-plane and the out-of-plane resistivities is found, as well as a signature of the substrate cubic to tetragonal transition. Both observations result from the structural distortion associated to the epitaxial strain. The low-temperature and field dependences of the Hall number are interpreted as due to the contribution of Coulomb interactions to weak localization, evidencing the strong correlations in this material. The introduction of a contribution from magnetic scatters, in the analysis of magnetoconductance in the weakly localized regime, is proposed as an alternative to an anomalously large temperature dependence of the Land{e} coefficient.
The crystallographic orientation of SrIrO3 surfaces is decisive for the occurrence of topological surface states. We show from DFT computations that (001) and (110) free surfaces have comparable energies, and, correspondingly, we experimentally observe that single micro-crystals exhibit both facet orientations. These surfaces are found to relax over typically the length of one oxygen octahedron, defining a structural critical thickness for thin films. A reconstruction of the electronic density associated to tilts of the oxygen octahedra is observed. On the other hand, thin films have invariably been reported to grow along the (110) direction. We show that the interfacial energy associated to the oxygen octahedra distortion for epitaxy is likely at the origin of this specific feature, and propose leads to induce (001) SrIrO3 growth.
We report proximity effects of spin-orbit coupling in EuO$_{1-x}$ films capped with a Pt overlayer. Transport measurements suggest that current flows along a conducting channel at the interface between the Pt and EuO. The temperature dependence of the resistivity picks up the critical behaviors of EuO, i.e., the metal-to-insulator transition. We also find an unusual enhancement of the magnetic anisotropy in this structure from its bulk value which results from strong spin-orbit coupling across the Pt/EuO interface.
We report on the synthesis of perovskite SrIrO3 thin films using sputtering technique. Single phase (110) oriented SrIrO$_3$ thin films were epitaxially grown on SrTiO3 (001) substrate. Using off-axis XRD $theta-2theta$ scans, we demonstrate that these films exhibit (110) out-of-plane orientation with (001) and (1-10) lying in-plane. The sputtering grown thin films have a smooth, homogeneous surface, and excellent coherent interface with the substrate.
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