Focus on recent advances in superconducting films

Superconducting films, their growth, characterization and optimization, are an inevitable part of modern research and development in the fields of superconductivity and solid-state physics in general. Due to their geometry and dimensionality, they offer possibilities for investigations and applications that would not be possible with single crystal or bulk polycrystalline samples. Well-known examples for applications are the functional layers of REBa2Cu3O7-δ (REBCO) in coated conductors, the microelectronic applications such as filters, SQUIDs and bolometers, and the superconducting layers in undulators. The non-equilibrium growth modes in certain deposition techniques offer the possibility to grow metastable phases or superconductors that are difficult to achieve in single crystal growth. The chemical and physical influence of the substrate allow the growth of new superconducting states such as ultra-thin FeSe with Tc's above 60 K or the recently discovered nickelates, as well as the alteration of the superconducting properties by static or dynamic epitaxial strain. The quality of superconducting films and their plenitude in research and applications grew constantly over the last years. This Focus Issue is to collect and show recent advances in the growth, characterisation and application of superconducting films. It may include: -advances in deposition techniques (ALD, CSD, MOCVD PLD, sputtering, etc. -advances in characterisation techniques of structural and electro-magnetic properties -High-Tc cuprate superconductors -Low-Tc superconductors and MgB2 -Fe-based superconductors -ultra-thin films -strain/pressure experiments