Synthesis and electronic transport of superconducting molybdenum nitride ultrathin crystalline platelets

Transition metal carbides (TMCs) and transition metal nitrides (TMNs) have been intensively studied in their bulk form due to their outstanding properties.¹ Xu et al.² established a liquid-metal-assisted chemical vapor deposition (LMCVD) method to grow large-area ultrathin Mo₂C and studied their robust superconducting properties down to a few nanometers in thickness. Wang et al.³ implemented a similar LMCVD approach to grow ultrathin MoN_x and studied their catalytic properties. However, to the best of our knowledge, the electronic properties such as the superconductivity of ultrathin MoN_x crystalline platelets have not been studied to date.

In our study, ultrathin MoN_x nanoplatelets were grown by LMCVD, and the morphology was characterized by scanning electron microscope, atomic force microscopy, and scanning/transmission electron microscope. Various flakes with different thicknesses were measured. For 120 nm thick platelets, the onset superconducting transition temperature was 12.11K which is comparable to the bulk Tc values, also showing a sharp transition width smaller than 0.1K, indicating a high degree of crystallinity. A magnetic field in the out-of-plane direction was applied and a series of magnetotransport measurements were performed. The linear temperature dependence behavior of the critical field is consistent with the 2D Ginzburg–Landau formalism for fields perpendicular to the planes, which supports the 2D nature of the superconducting state. By linear fitting the Hc with Tc, we extrapolated the zero-temperature critical field to be around 3.79T and the Ginzburg-Landau coherence length at zero temperature to be around 9.3 nm. By analyzing the results from Hall measurements and the longitudinal resistance measurements, the mean free path was estimated to be > 100nm, an order of magnitude higher than the Ginzburg-Landau coherence length, exceeding the superconducting clean limit.

In summary, we have successfully synthesized ultrathin MoN_x nanoplatelets through an LMCVD method and conducted electronic transport measurements. We plan to also apply an in-plane magnetic field to probe the anisotropy and dimensionality of the superconducting state.