Superconductivity in Uniquely Strained RuO$_{2}$ Films

TL;DR

This study demonstrates that strain engineering in epitaxial RuO₂ films can induce superconductivity, highlighting the role of lattice modifications and phonon modes, and suggesting potential for tuning superconductivity in simple oxides.

Contribution

It reveals how epitaxial strain affects superconductivity in RuO₂ films and emphasizes the importance of soft phonon modes, providing new pathways for exploring superconductivity in transition metal oxides.

Findings

Superconductivity correlates with specific lattice parameter changes.

Shortening Ru-O bonds is linked to superconductivity.

Soft phonon modes are crucial for the emergence of superconductivity.

Abstract

We report strain engineering of superconductivity in RuO$_2$ singlecrystalline films, which are epitaxially grown on rutile TiO$_2$ and MgF$_2$ substrates with various crystal orientations. Systematic mappings between the superconducting transition temperature and the lattice parameters reveal that shortening of specific ruthenium-oxygen bonds is a common feature among the superconducting RuO$_2$ films. Ab initio calculations of electronic and phononic structures for the strained RuO$_2$ films suggest the importance of soft phonon modes for emergence of the superconductivity. The findings indicate that simple transition metal oxides such as with the rutile structure may be suitable for further exploring superconductivity by controlling phonon modes through the epitaxial strain.