  The double Gamow-Teller strength distributions in the lightest double
beta-decay candidate $^{48}$Ca and its isotope $^{46}$Ca were calculated using
the nuclear shell model by applying the single Gamow-Teller operator two times
sequentially on the ground state of parent nucleus. The nuclear matrix element
of the double Gamow-Teller transition from the ground state to the ground state
that goes into the double beta decay calculation was shown as a small fraction
of the total transition.
