t+t clustering states in He-isotopes

t+t clustering states in He isotopes are investigated by using two theoretical approaches. We obtained many t+t resonances near to the t+t threshold with a RGM type approach. Further, a role of the t+t cluster component in the ground state is examined with AMD triple-S, allowing the wider configuration space containing simultaneously the 't+t+valence neutrons' structure and '4He+valence neutrons' structure. We understand the importance of the t+t component even for the ground state