Superconductivity Induced by Site-Selective Arsenic Doping in Mo${}_5$Si${}_3$

Arsenic doping in silicides has been much less studied compared with phosphorus. In this study, superconductivity is successfully induced by As doping in Mo${}_5$Si${}_3$. The superconducting transition temperature ($T_c$) reaches 7.7 K, which is higher than those in previously known W${}_5$Si${}_3$-type superconductors. Mo${}_5$Si${}_2$As is a type-II BCS superconductor with upper and lower critical fields of 6.65 T and 22.4 mT, respectively. In addition, As atoms are found to selectively take the 8$h$ sites in Mo${}_5$Si${}_2$As. The emergence of superconductivity is possibly due to the shift of Fermi level as a consequence of As doping, as revealed by the specific heat measurements and first-principles calculations. Our work provides not only another example of As doping, but also a practical strategy to achieve superconductivity in silicides through Fermi level engineering.