Preparation and physical property tuning of superconducting nickelate thin films via oxide molecular-beam epitaxy

Superconducting nickelates are another important class of layered oxide superconductors discovered after cuprates， providing a brand-new material platform for exploring the microscopic mechanisms of high-temperature superconductivity. In recent years， superconductivity has been successively observed in square-planar and Ruddlesden-Popper nickelates，making the nickelate family a rapidly developing field in condensed matter physics. However，the macroscopic physical properties of superconducting nickelate thin films are extremely sensitive to stoichiometry，interface structure，strain state，and oxygen content. Oxide molecular-beam epitaxy（OMBE），with its capability for atomic-level precise control of composition，interface structure，and in situ monitoring，plays an important role in the growth of high-quality thin films. This article first briefly reviews the history and basic principles of OMBE，then summarizes its latest applications in the preparation of superconducting nickelate thin films. In-depth discussions are focused on key issues including stoichiometry control，polar-interface engineering，in situ topotactic reduction，synthesis of freestanding membranes， optimization of atomic-layer deposition sequences，and heterovalent cation doping. Finally，the prospects of this technology for structural design and property manipulation of superconducting nickelates are discussed.