Quantum phase transitions driven by rhombic-type single-ion anisotropy in the S=1 Haldane chain
AbstractThe spin-1 Haldane chain is an example of the symmetry-protected-topological (SPT) phase in one dimension. Experimental realization of the spin chain materials usually involves both the uniaxial-type, D(Sz)2, and the rhombic-type, E[(Sx)2−(Sy)2], single-ion anisotropies. Here, we provide a precise ground-state phase diagram for a spin-1 Haldane chain with these single-ion anisotropies. Using quantum numbers, we find that the Z2 symmetry breaking phase can be characterized by double degeneracy in the entanglement spectrum. Topological quantum phase transitions take place on particular paths in the phase diagram, from the Haldane phase to the large-Ex, large-Ey, or large-D phases. The topological critical points are determined by the level spectroscopy method with a newly developed parity technique in the density matrix renormalization group [Phys. Rev. B 86, 024403 (2012)PRBMDO1098-012110.1103/PhysRevB.86.024403], and the Haldane-large-D critical point is obtained with an unprecedented precision, (D/J)c=0.9684713(1). Close to this critical point, a small rhombic single-ion anisotropy |E|/J≪1 can destroy the Haldane phase and bring the system into a y-Néel phase. We propose that the compound [Ni(HF2)(3-Clpy)4]BF4 is a candidate system to search for the y-Néel phase.