Crystal orientation-dependent superconductivity in titanium nitride films

High-quality titanium nitride (TiN) films with different crystal orientations (001, 110, and 111) obtained under the same growth conditions are systematically investigated by both ultra-low temperature scanning tunneling microscope/spectroscopy and transport experiments. Our results reveal that all of them are conventional type-II superconductors, which exhibit spatially homogeneous superconducting properties. The superconductivity is uniform between surface and bulk. Intriguingly, the TiN (111) film has the highest transition temperature (T-c) but the lowest upper critical field (H-c2). This crystal orientation-dependent superconductivity could be explained by the fact that TiN (001) and TiN (110) films are dirtier than TiN (111). Our results suggest that (111)-oriented TiN is superior to design certain superconducting devices, including Josephson junction devices. The crystallographic orientation could offer an effective controlling parameter for designing TiN-based superconducting devices.