Four-body cluster structure of $A=7-10$ double-$Λ$ hypernuclei

Energy levels of the double-$Λ$ hypernuclei $_Λ^{}$$_Λ^7$He, $_Λ^{}$$_Λ^7$Li, $_Λ^{}$$_Λ^8$Li, $_Λ^{}$$_Λ^9$Li, $_Λ^{}$$_Λ^9$Be and $_Λ^{}$$_Λ^{10}$Be are predicted on the basis of the $α+x+Λ+Λ$ four-body model with $x=n, p, d, t, ^3$He and $α$, respectively.