Abstract Body

As the representative of the transition metal carbide, molybdenum carbide (Mo₂C) has been explored for applications in catalysts, energy storage, and superconductivity. Generally, selectively etching Ga from Mo₂Ga₂C in HF solution is the most popular method for synthesizing Mo₂CT_x, where T_x represents the surface functional group (-O, -OH, -F)^[1]. The existence of functional groups on their surface strongly influences the Fermi level density of states and thereby the electronic conductivity^[2]. Therefore, tailoring the surface functionalization demonstrates excellent potential for tuning the superconductivity of Mo2C. In this study, we systematically investigated the superconductivity of Mo₂C by fluorine doping. Mo₂C was synthesized by the topochemical method, in which Mo₂C can be transformed from pristine MoS₂ without using HF. NH4F was considered a fluorine source and F-doped Mo₂C was obtained by sintering the mixture of Mo₂C and NH₄F in different ratios.

The superconducting transition temperature (T_c) of the Mo₂C sample was measured by using the zero-field cooling (ZFC) and field cooling (FC) modes; the value of H was 10 Oe. The values of T_c were determined from the M/H – T plot in ZFC mode. As shown in Fig. 1, the superconductivity of Mo₂C was enhanced by increasing the content of fluorine and reached the highest Tc value of 5.7 K, in comparison with 3.2 K of Mo₂C without F doping. The M – H loop of F-Mo₂C, recorded at 3.0 K, illustrated a clear hysteresis loop, indicating a type-II superconductor.

References

[1] James L. Hart et al. Nat. Commun. 10, 522 (2019).
[2] Dmitri V. Talapin et al. Science. 369, 979 (2020).

Acknowledgment

This work was supported by a talent training fund (YK2110) from Northwest Institute for Non-ferrous Metal Research.