Superconductivity in Uniquely Strained RuO2 Films

We report strain engineering of superconductivity in RuO$_2$\nsinglecrystalline films, which are epitaxially grown on rutile TiO$_2$ and\nMgF$_2$ substrates with various crystal orientations. Systematic mappings\nbetween the superconducting transition temperature and the lattice parameters\nreveal that shortening of specific ruthenium-oxygen bonds is a common feature\namong the superconducting RuO$_2$ films. Ab initio calculations of electronic\nand phononic structures for the strained RuO$_2$ films suggest the importance\nof soft phonon modes for emergence of the superconductivity. The findings\nindicate that simple transition metal oxides such as with the rutile structure\nmay be suitable for further exploring superconductivity by controlling phonon\nmodes through the epitaxial strain.\n