Tip-induced superconductivity on the topological semimetals TaAs2 and NbAs2

${\mathrm{TaAs}}₂$ and ${\mathrm{NbAs}}₂$ are members of the ${MPn}₂$ family with weak topological invariants of ${Z}₂$ = [0;111]. Here, we report the tip-induced superconductivity achieved on both materials using the point-contact technique. Although the weak ${Z}₂$ number leads to strongly crystal-orientation-dependent surface states, we observed a universal relationship between the zero-temperature upper critical field ${H}_c2(0)$ and the critical temperature ${T}_c$ for different crystal orientations. Combined with first-principles calculations, the findings here could identify a bulk band, instead of the much speculated surface bands, playing the dominant role in the induced superconductivity. These results predict a great possibility to realize superconductivity in other members of the ${MPn}₂$ family possessing similar band structures and provide clues to understand the mechanism of tip-induced superconductivity.