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Register a new userNovel Layered Iridate Ba7Ir3O13+{delta} Thin Films with Colossal Permittivity
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Ba7Ir3O13+{delta} in thin film form is discovered. These films are characterized by colossal permittivity (CP) ~104 at room temperature, attributable to the colossal internal barrier layer capacitance effect at atomically thin domain boundaries. These findings suggest a new route to seeking novel CP materials through designing atomically thin domain boundaries.
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We theoretically study the magnon spin thermal transport using a strong coupling approach in pyrochlore iridate trilayer thin films grown along the [111] direction. As a result of the Dzyaloshinskii-Moriya interaction (DMI), the spin configuration of the ground state is an all-in/all-out ordering on neighboring tetrahedra of the pyrochlore lattice. In such a state, the system has an inversion symmetry and a Nernst-type thermal spin current response is well defined. We calculate the temperature dependence of the magnon Nernst response with respect to the magnon band topology controlled by the spin-orbit coupling parameters and observe topologically protected chiral edge modes over a range of parameters. Our study complements prior work on the magnon thermal Hall effect in thin-film pyrochlore iridates and suggests that the [111] grown thin-film pyrochlore iridates are a promising candidate for thermal spin transport and spin caloritronic devices.
While pyrochlore iridate thin films are theoretically predicted to possess a variety of emergent topological properties, experimental verification of these predictions can be obstructed by the challenge in thin film growth. Here we report on the pulsed laser deposition and characterization of thin films of a representative pyrochlore compound Bi2Ir2O7. The films were epitaxially grown on yttria-stabilized zirconia substrates and have lattice constants that are a few percent larger than that of the bulk single crystals. The film composition shows a strong dependence on the oxygen partial pressure. Density-functional-theory calculations indicate the existence of Bi_Ir antisite defects, qualitatively consistent with the high Bi: Ir ratio found in the films. Both Ir and Bi have oxidation states that are lower than their nominal values, suggesting the existence of oxygen deficiency. The iridate thin films show a variety of intriguing transport characteristics, including multiple charge carriers, logarithmic dependence of resistance on temperature, antilocalization corrections to conductance due to spin-orbit interactions, and linear positive magnetoresistance.
Inversion symmetry breaking is a ubiquitous concept in condensed-matter science. On the one hand, it is a prerequisite for many technologically relevant effects such as piezoelectricity, photovoltaic and nonlinear optical properties and spin-transport phenomena. On the other hand, it may determine abstract properties such as the electronic topology in quantum materials. Therefore, the creation of materials where inversion symmetry can be turned on or off by design may be the ultimate route towards controlling parity-related phenomena and functionalities. Here, we engineer the symmetry of ultrathin epitaxial oxide films by sub-unit-cell growth control. We reversibly activate and deactivate inversion symmetry in the layered hexagonal manganites, h-RMnO$_3$ with R = Y, Er, Tb. While an odd number of half-unit-cell layers exhibits a breaking of inversion symmetry through its arrangement of MnO$_5$ bipyramids, an even number of such half-unit-cell layers takes on a centrosymmetric structure. Here we control the resulting symmetry by tracking the growth in situ via optical second-harmonic generation. We furthermore demonstrate that our symmetry engineering works independent of the choice of R and even in heterostructures mixing constituents with different R in a two-dimensional growth mode. Symmetry engineering on the atomic level thus suggests a new platform for the controlled activation and deactivation of symmetry-governed functionalities in oxide-electronic epitaxial thin films.
Single-crystalline transition metal films are ideal playing fields for the epitaxial growth of graphene and graphene-base materials. Graphene-silicon layered structures were successfully constructed on Ir(111) thin film on Si substrate with an yttria-stabilized zirconia buffer layer via intercalation approach. Such hetero-layered structures are compatible with current Si-based microelectronic technique, showing high promise for applications in future micro- and nano-electronic devices.
It has been well established that both in bulk at ambient pressure and for films under modest strains, cubic SrCoO$_{3-delta}$ ($delta < 0.2$) is a ferromagnetic metal. Recent theoretical work, however, indicates that a magnetic phase transition to an antiferromagnetic structure could occur under large strain accompanied by a metal-insulator transition. We have observed a strain-induced ferromagnetic to antiferromagnetic phase transition in SrCoO$_{3-delta}$ films grown on DyScO$_3$ substrates, which provide a large tensile epitaxial strain, as compared to ferromagnetic films under lower tensile strain on SrTiO$_3$ substrates. Magnetometry results demonstrate the existence of antiferromagnetic spin correlations and neutron diffraction experiments provide a direct evidence for a G-type antiferromagnetic structure with Neel temperatures between $T_N sim 135,pm,10,K$ and $sim 325,pm,10,K$ depending on the oxygen content of the samples. Therefore, our data experimentally confirm the predicted strain-induced magnetic phase transition to an antiferromagnetic state for SrCoO$_{3-delta}$ thin films under large epitaxial strain.
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