Observation of the β-delayed γ-proton decay of (56)Zn and its impact on the Gamow-Teller strength evaluation.

We report the observation of a very exotic decay mode at the proton drip line, the β-delayed γ-proton decay, clearly seen in the β decay of the T_{z}=-2 nucleus ^{56}Zn. Three γ-proton sequences have been observed after the β decay. Here this decay mode, already observed in the sd shell, is seen for the first time in the fp shell. Both γ and proton decays have been taken into account in the estimation of the Fermi and Gamow-Teller strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.