Inducing strong superconductivity in WTe₂ by proximity effect

The superconducting states inheriting nontrivial topology at interfaces are expected to exhibit exotic phenomena such as topological superconductivity and Majorana zero modes, which hold promise for applications in quantum computation. However, a practical realization of such hybrid structures based on topological semimetals and superconductors has hitherto been limited. Here, we report the strong proximity-induced superconductivity in type-II Weyl semimetal WTe2. When the WTe2 thickness (t_(WTe_2 )) reaches 21 nm, the superconducting transition occurs around the critical temperature (T_c) of NbSe2 with a gap amplitude (Δ_p) of 0.38 meV and an unexpected ultra-long proximity length. Our theoretical calculations, based on the Bogoliubov-de Gennes equations in the clean limit, predict that the induced superconducting gap is a sizable fraction of the NbSe2 superconducting one when t_(WTe_2 ) is less than 30 nm, and then decreases quickly as t_(WTe_2 ) increases. This agrees qualitatively well with the experiments. Such observations demonstrate a new direction in the search for superconducting phases in topological semimetals.