Topological materials are derived from the interplay between symmetry and topology. Advances in topological band theories have led to the prediction that the antiperovskite oxide Sr3SnO is a topological crystalline insulator, a new electronic phase of matter where the conductivity in its (001) crystallographic planes is protected by crystallographic point group symmetries. Realization of this material, however, is challenging. Guided by thermodynamic calculations, a deposition approach is designed and implemented to achieve the adsorption‐controlled growth of epitaxial Sr3SnO single‐crystal films by molecular‐beam epitaxy (MBE). In situ transport and angle‐resolved photoemission spectroscopy measurements reveal the metallic and electronic structure of the as‐grown samples. Compared with conventional MBE, the used synthesis route results in superior sample quality and is readily adapted to other topological systems with antiperovskite structures. The successful realization of thin films of Sr3SnO opens opportunities to manipulate topological states by tuning symmetries via strain engineering and heterostructuring.
Spatially resolved photoluminescence (PL) of methylammonium lead iodide (MAPbI3) films in planar heterojunction solar cells is probed by time-resolved confocal microscopy to study the interface effect on PL intensity-voltage (PL-V) hysteresis. Negligible PL-V hysteresis is observed at the interfacial area, while significant hysteresis is observed in the bulk film. PL lifetime imaging of the perovskite device reveals inhomogeneous charge extraction due to variation of the interfacial contact quality. Poor interfacial contact leads to more severe PL-V hysteresis in the bulk perovskite film. The PL-V characteristics also suggest that voltage-driven ion migration may lead to redistribution of charge traps, and consequently affect the nonradiative charge recombination and the PL intensity in MAPbI3 films.
The emergence of artificial intelligence and machine-learning-based systems, in conjunction with the pervasive implementation of the internet of things has put a strong emphasis on the energy efficiency of computing. This has triggered research on multiple pathways to improve computing efficiency, spanning 3-D integration of logic and memory as well as new, physics-based pathways including those embracing the electron’s spin degree of freedom, namely spintronics. Concurrently, the proposed integration of superconductivity and spintronics emphasizes complex oxides as a promising platform which in principle can integrate spin current manipulation and high temperature superconductivity within the same complex system. Here, we report giant spin-orbit torque (SOT) discovered in the normal state of a complex oxide superconductor, Ba(Pb,Bi)O3, which provides isotropic and easily manipulated superconducting properties. Using spin-torque ferromagnetic resonance (ST-FMR) and d.c. non-linear Hall measurements, we find a robust SOT efficiency exceeding unity and demonstrate current driven magnetization switching at current densities as low as \(4\times {10}^{5}\text{A}{\text{c}\text{m}}^{-2}\). The hybridized s-p orbital character at the Fermi energy makes this an unexpectedly large value. We postulate the presence of an unconventional SOT generation in bismuthate heterostructures and anticipate our results will trigger further exploration of such complex oxides for the development of superconducting spintronics.
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