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Dilute PbMn alloys have been prepared in a 3 He/ 4 He-dilution cryostat by low-temperature implantation of Mn + ions into annealed PI? films forming the counter electrode of Mg-MgO-Pb tunnel junctions. The tunnel conductance as a function of the Mn concentration was measured at 200 mK. Two pronounced impurity bands are found within the superconducting gap at OJ/A= 0.23 and 0.79, respectively. The results can be described by existing theories if scattering of different partial waves is taken into account.PACS numbers: 74.50.+ r, 61.70.Tm, 75.20.Since the pioneering work of Abrikosov and Gor'kov (AG) 1 on the pair-breaking behavior of magnetic impurities dissolved into a superconductor, much progress has been achieved in the theoretical description of such systems. This includes an extension of the AG perturbational treatment beyond second order for classical spins (J-0, S -°°, JS = const, J the exchange constant, S the impurity spin) as formulated independently by Shiba 2 and Rusinov, 3 as well as theories taking into account the Kondo effect in case of J<0 (Muller-Hartmann, Zittartz, and Bringer, MHZB). 4 * 5 Very recently theories also have appeared which include a possible strongcoupling behavior of the superconducting matrix. 6 One of the striking features of these improved theories is the prediction of an impurity band due to localized states within the gap of the superconductor. Even different bands should be possible, if partial waves corresponding to I >0 are involved in the scattering process.Experimentally bound states within the gap have been observed in Kondo systems, where superconductivity was induced by the proximity effect. 7 In addition, various experiments by Ginsberg and co-workers 8 * 9 gave strong experimental evidence on these bound states in homogeneous alloys of InMn and PbMn. Here the samples were prepared by quench condensation and thus the matrices were highly disordered. As an alternative preparation technique, low-temperature ion implantation can be used. This method offers the following advantages: One can start with wellannealed films; at low temperature, solubility limits can be overcome and the concentration of the magnetic impurities can be varied continuously within the same sample. Using this technique Heim et al. 10 could explain their results on PbMn by bound states in the gap, but because of the large temperature smearing at T= 1.2 K these states could not be resolved by tunneling. HrIn this Letter we report on an improved experiment, using low-temperature implantation of Mn + ions into well-annealed Pb films to prepare dilute PbMn alloys within a 3 He/ 4 He-dilution refrigerator. In this way, for the first time, impurity bands within the superconducting gap of PbMn could be clearly resolved by electron tunneling.For each experiment two tunneling junctions of the type Mg-MgO-Pb were prepared simultaneously on a glass substrate in a separate evaporation system. The geometrical arrangement can be found in Ref. 11. After junctions were mounted onto the mixing chamber of a 3 He/ ...