Superconductivity in thin films of RuN

Superconductivity has been found in RuN films obtained by reactive magnetron sputtering. This novel member of the metal nitride superconductors family has a critical temperature of the superconducting transition that varies depending on the substrate, ranging from 0.77 K to 1.29 K. The parameters of the crystal lattice of the superconducting films have been determined: The lattice is cubic with rhombohedral distortion along the normal to substrate surface with parameters $a=b=c=4.559\phantom{\rule{0.16em}{0ex}}\mathrm{\AA{}}$ for $\mathrm{RuN}/{\mathrm{SiO}}₂$, $a=b=c=4.536\phantom{\rule{0.16em}{0ex}}\mathrm{\AA{}}$ for RuN/Si, and $\ensuremath{\alpha}=\ensuremath{\beta}=\ensuremath{\gamma}=87.{96}^{\ensuremath{\circ}}$ for both films. The upper critical magnetic field at zero temperature ${H}_c2(0)=2.3--4.1\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ found by extrapolation our experimental data collected at $T⪆0.8$ to zero temperature using the WHH model is near the upper paramagnetic limit. An $s$-wave single-band energy gap of $\mathrm{\ensuremath{\Delta}}(0)=0.19\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ was revealed by self-field critical current experiment at temperatures down to 10 mK.