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Two-dimensional (2D) material such as graphene,black phosphorus,and layered transition metal dichalcogenides (TMDs) have attracted enormous interest for their unique structure,novel physical properties,and broad potential applications.Superior to semimetallic graphene,few-layer MoS2s show moderate band gaps which are crucial for practical on/off ratios in electronic circuit devices[1].Besides,MoS2 is potentially important in optoelectronics because its band gap is in the visible light range[2].For this reason,great efforts have been made to investigate the dynamics of various carriers in MoS2 including mobilities of electrons,excitons,and phonons.Recently,the electron-doped monolayer MoS2 was predicted to be a BCS-type superconductor with a considerable critical temperature (Tc) up to 20 K when one extra electron is artificially added per chemical unit[3].However,by considering realistic doping methods (e.g.,K absorption)[3],the calculated Tc was far below the expected value.Experimentally,an early work by Woollam et al.studied the insertion of K/Na atoms into bulk MoS2,which found the maximum superconducting Tcs of KxMoS2 and NaxMoS2 to be about 7 K and 3.2 K,respectively[4].In this sense,the electron-doped MoS2 should be a promising superconductor although its real Tc is seriously suppressed by real doping methods.In this work[5],the electronic structure and lattice dynamics of MoX2 (X=S and Se) bilayers with monolayer Na intercalated have been calculated via first-principles density functional theory (DFT) and density functional perturbation theory (DFPT).According to the electron-phonon interaction,it is predicted that these bilayers can be transformed from indirect-gap semiconductors to superconductors by Na intercalation.More interestingly,the biaxial tensile strain can significantly enhance the superconducting temperature up to about 10 K in Na-intercalated MoS2.In addition,the phonon mean free path at room temperature is also greatly improved in Na-intercalated MoSe2,which is advantageous for related applications.