Quantum phase transitions and the 1/3 magnetization plateau in the spin-1/2 Ferromagnetic-Ferromagnetic-Antiferromagnetic chain

The ground-state properties of the spin-1/2 Ferromagnetic-Ferromagnetic-Antiferromagnetic (F-F-AF) trimerized chain are investigated by the infinite time-evolving block decimation (iTEBD) method. A ground-state phase diagram including three different phases, i.e., a fully polarized phase, a 1/3 plateau phase, and a non-plateau phase, is obtained. All the quantum phase transitions (QPTs) can be described well by the model independent bipartite entanglement. QPTs between the non-plateau phase and the other two phases belong to the second-order category. Doubly degenerate entanglement spectrum and nontrivial string order are observed in the 1/3 plateau phase, which can be used to distinguish it from the other phases. By the scaling behavior of the bipartite entanglement, the central charge of the critical non-plateau phase is determined to be c≃ 1.