Seminarium Fizyki Materii Skondensowanej

In this work, we investigate the low-energy properties of the dimerized frustrated ferromagnetic (FM) J1−J′1−J2 model with the density matrix renormalization group method. We show the ground state phase diagram spanned by a wide range of J'1/J1 and /J2|J1|features ferromagnetic phase and valence bond solid (VBS) phases that are continuations from the J'1/J1 limits of the model. In the limit J'1/J1=1 we recover FM J1-J2 model hosting $\mathcal{D}_3$-VBS state where valence bonds form between third-neighbor spins. The other VBS phase named mixed-VBS features both second- and third neighboring spins that continue from the J'1/J1=0 limit. We show that both phases feature hidden antiferromagnetic order and twofold degeneracy in the entanglement spectrum characterizing them as Haldane states. Remarkably, we encounter a nontrivial quantum phase transition between two topological VBS states, where at the boundary of phases VBS stability is enhanced.We discuss results in the context of other spin chain models and edge-sharing cuprate materials.