Magnetic phase diagram of a frustrated ferrimagnetic ladder: Relation to the one-dimensional boson Hubbard model

We study the magnetic phase diagram of two coupled mixed-spin $(1,1\mathrm{/}2)$ Heisenberg chains as a function of the frustration parameter related to diagonal exchange couplings. The analysis is performed by using spin-wave series and exact numerical diagonalization techniques. The obtained phase diagram–containing the Luttinger liquid phase, the plateau phase with a magnetization per rung $M=1\mathrm{/}2$, and the fully polarized phase–is closely related to the generic $(J\mathrm{/}U,\mu \mathrm{/}U)$ phase diagram of the one-dimensional boson Hubbard model.