Spin-wave theory from the fully polarized vacuum for ferrimagnetic spin-(1/2, S) chains in a magnetic field

We compare the ground-state features of alternating ferrimagnetic chains (1/2, S) with S = 1, 3/2, 2, 5/2 in a magnetic field and the corresponding Holstein-Primakoff bosonic models up to order (s/S)^1/2 considering the fully polarized magnetization as the boson vacuum. The single-particle Hamiltonian is the Rice-Mele model with uniform hopping and modified boundaries, while the interactions have a correlated (density-dependent) hopping term and magnon-magnon repulsion. We use density matrix renormalization group calculations to show the quantitative agreement between the results from the spin model and the full bosonic approximation. In particular, we verify the good accordance in the behavior of the edge states, associated with the ferrimagnetic plateau, from the two models. Furthermore, we show that the boundary magnon density strongly depends on the interactions and particle statistics.