Impurity Resonance States in Bi 2 Sr 1.6 La 0.4 CuO 6+ δ

Using scanning tunneling spectroscopy (STS) at 4.2 K, we observed impurity resonance in single crystals of Zn doped Bi 2 Sr 1.6 La 0.4 CuO 6+ δ ( T C =28 K) (Bi2201). Many impurity resonances characterized by the peak structure near E F were observed. We found that the number of the resonances was less than that of the doped impurities (0.45 % determined by inductively coupled plasma optical emission spectrometry). The resonance peaks were observed only in the region having smaller gap less than Δ cut ∼26 meV. This Δ cut was about half of that reported in Bi 2 Sr 2 CaCu 2 O 8+ δ .