Impurity-induced resonant states in topological nodal-line semimetals

Nodal-line semimetals are characterized by a kind of topologically nontrivial bulk-band crossing, giving rise to almost flat surface states. Notably, direct evidence of the surface states is still awaited. Here we theoretically study impurity effects in topological nodal-line semimetals based on the T-matrix method. It is found that some low energy states may be induced near the impurity site for a bulk impurity, while the visible resonant impurity state can only exist for certain impurity strength. For a surface impurity, a robust resonant impurity state exists in a wide parametric range of impurity strength. Such robust resonant state stems from the topologically protected weak dispersive surface states, which can be probed by scanning tunneling microscopy, providing a clear signature of the topological surface states in the nodal-line semimetals.