Tuning superconductivity in vanadium nitride films by adjusting strain

Transition-metal nitrides (TMNs) are enriched with various exotic phenomena such as superconductivity and quantum magnetism. Vanadium nitride (VN) is a typical superconducting TMN, with its superconductivity sensitively associated with various physical and chemical factors including nitrogen vacancies and lattice constants. Strain tuning is a convenient and effective method to manipulate the superconducting behavior of VN in the thin-film form, providing an additional tuning knob for potential applications in quantum computing and passive microwave devices. Here, we demonstrate the effect of strain tuning on VN films both statically and dynamically. By depositing on various substrates, the static strain states of VN films can be controlled from $\ensuremath{-}4.04%$ (compressive) to $+2.0%$ (tensile), making the superconducting transition temperature $({T}_{c})$ tunable by approximately $\ifmmode\pm\else\textpm\fi{}10%$. Applying in situ dynamic compressive strain via a piezoelectric substrate, we are able to achieve control of ${T}_{c}$ by a step as fine as 10 mK. Furthermore, our first-principles calculations point out that the strain-tuning effect of ${T}_{c}$ originates from a change in the density of states for vanadium's d orbitals.