Electronic band structures in solids stem from a periodic potential reflecting the structure of either the crystal lattice or electronic order. In the stoichiometric ruthenate Ca3Ru2O7, numerous Fermi surface-sensitive probes indicate a low-temperature electronic reconstruction. Yet, the causality and the reconstructed band structure remain unsolved. Here, we show by angle-resolved photoemission spectroscopy, how in Ca3Ru2O7 a C2-symmetric massive Dirac semimetal is realized through a Brillouin-zone preserving electronic reconstruction. This Dirac semimetal emerges in a two-stage transition upon cooling. The Dirac point and band velocities are consistent with constraints set by quantum oscillation, thermodynamic, and transport experiments, suggesting that the complete Fermi surface is resolved. The reconstructed structure—incompatible with translational-symmetry-breaking density waves—serves as an important test for band structure calculations of correlated electron systems.
By using mostly the muon-spin rotation/relaxation (µSR) technique, we investigate the superconductivity (SC) of Nb 5 Ir 3−x Pt x O (x = 0 and 1.6) alloys, with T c = 10.5 K and 9.1 K, respectively. At a macroscopic level, their superconductivity was studied by electrical resistivity, magnetization, and specific-heat measurements. In both compounds, the electronic specific heat and the low-temperature superfluid density data suggest a nodeless SC. The superconducting gap value and the specific heat discontinuity at T c are larger than that expected from the Bardeen-Cooper-Schrieffer theory in the weak-coupling regime, indicating strongcoupling superconductivity in the Nb 5 Ir 3−x Pt x O family. In Nb 5 Ir 3 O, multigap SC is evidenced by the field dependence of the electronic specific heat coefficient and the superconducting Gaussian relaxation rate, as well as by the temperature dependence of the upper critical field. Pt substitution suppresses one of the gaps, and Nb 5 Ir 1.4 Pt 1.6 O becomes a single-gap superconductor. By combining our extensive experimental results, we provide evidence for a multiple-to single-gap SC crossover in the Nb 5 Ir 3−x Pt x O family.
Charge‐transfer phenomena at heterointerfaces are a promising pathway to engineer functionalities absent in bulk materials but can also lead to degraded properties in ultrathin films. Mitigating such undesired effects with an interlayer reshapes the interface architecture, restricting its operability. Therefore, developing less‐invasive methods to control charge transfer will be beneficial. Here, an appropriate top‐interface design allows for remote manipulation of the charge configuration of the buried interface and concurrent restoration of the ferromagnetic trait of the whole film. Double‐perovskite insulating ferromagnetic La2NiMnO6 (LNMO) thin films grown on perovskite oxide substrates are investigated as a model system. An oxygen‐vacancy‐assisted electronic reconstruction takes place initially at the LNMO polar interfaces. As a result, the magnetic properties of 2–5 unit cell LNMO films are affected beyond dimensionality effects. The introduction of a top electron‐acceptor layer redistributes the electron excess and restores the ferromagnetic properties of the ultrathin LNMO films. Such a strategy can be extended to other interfaces and provides an advanced approach to fine‐tune the electronic features of complex multilayered heterostructures.
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