Impurity effects of the Λ particle on the 2 α cluster states of Be 9 and Be 10

The low-lying structures of $_{\mathrm{\ensuremath{\Lambda}}}^{10}\mathrm{Be}$ and $_{\mathrm{\ensuremath{\Lambda}}}^{11}\mathrm{Be}$ are investigated within the framework of the antisymmetrized molecular dynamics. We focus on the modifications of the excitation spectra and dynamical changes of the $2\ensuremath{\alpha}$ cluster structure caused by a $\mathrm{\ensuremath{\Lambda}}$ particle as an impurity in these hypernuclei. It is found that the excitation energies of well-pronounced cluster states are largely shifted up by the addition of a $\mathrm{\ensuremath{\Lambda}}$ particle. Furthermore, we also find that the $2\ensuremath{\alpha}$ cluster structure is significantly changed in the excited states, whereas it is almost unchanged in the ground states.