The mass-imbalanced fermionic mixture is studied, where N≤5 identical fermions interact resonantly with an impurity, a distinguishable atom. The shell structure is explored, and the physics of a dynamic light-impurity is shown to be different from that of the static heavy-impurity case. The energies in a harmonic trap at unitarity are calculated and extrapolated to the zero-range limit. In doing so, the scale factor of the ground state, as well as of a few excited states, is calculated. In the 2≤N≤4 systems, pure (N+1) Efimov states exist for large enough mass ratio. However, no sign for a six-body Efimov state in the (5+1) system is found in the mass ratio explored, M/m≤12.
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