Diversity of quantum ground states and quantum phase transitions of a spin- 12 Heisenberg octahedral chain

Abstract

The spin- 2Heisenberg octahedral chain with regularly alternating monomeric and squareplaquette sites is investigated using various analytical and numerical methods: variational technique, localized-magnon approach, exact diagonalization (ED) and density-matrix renormalization group (DMRG) method. The model belongs to the class of flat-band systems and it has a rich ground-state phase diagram including phases with spontaneously broken translational symmetry. Moreover, it exhibits an anomalous low-temperature thermodynamics close to continuous or discontinuous fielddriven quantum phase transitions between three quantum ferrimagnetic phases, tetramer-hexamer phase, monomer-tetramer phase, localized-magnon phase and two different spin-liquid phases. If the intra-plaquette coupling is at least twice as strong as the monomer-plaquette coupling, the variational method furnishes a rigorous proof of the monomer-tetramer ground state in a low-field region and the localized-magnon approach provides an exact evidence of a single magnon trapped at each square plaquette in a high-field region. In the rest of parameter space we have numerically studied the ground-state phase diagram and magnetization process using DMRG and ED methods. It is shown that the zero-temperature magnetization curve may involve up to four intermediate plateaus at zero, one-fifth, two-fifth and three-fifth of the saturation magnetization, while the specific heat exhibits a striking low-temperature peak in a vicinity of discontinuous quantum phase transitions.

Cluster-based Haldane phases, bound magnon crystals and quantum spin liquids of a mixed spin-1 and spin-1/2 Heisenberg octahedral chain

“…[26][27][28] In our recent work, we have found that the localized-magnon approach can be extended to cover a full magnetization curve of the spin-1/2 Heisenberg octahedral chain from zero up to saturation field whenever the lowest-energy bound one-and two-magnon states are simultaneously taken into consideration. 29,30 The present work will be devoted to a detailed examination of the mixed spin-1 and spin-1/2 Heisenberg octahedral chain in a magnetic field. It will be demonstrated hereafter that the considered quantum spin chain exhibits a lot of intriguing quantum ground states including the cluster-based Haldane phases, the bound magnoncrystal phases, the Lieb-Mattis ferrimagnetic phases and the Tomonaga-Luttinger quantum spin liquids, which will be the main subject of our investigations.…”

Magnetic-field–temperature phase diagram of alternating ferrimagnetic chains: Spin-wave theory from a fully polarized vacuum

“…A minimum in the m(T ) curve is also observed for B = B i , due to the O(T 3 ) in Eq. (35), as shown in Fig. 5(d).…”

Magnetic phase diagrams of the spin-$\frac{1}{2}$ Heisenberg model on a kagome-strip chain: Emergence of a Haldane phase

“…In addition, the Heisenberg models describing frustrated quantum spin chains are known to exhibit various types of quantum phases, which have been studied intensively. Magnetization plateaus and strong quantum entanglement states due to the competition between frustration and quantum fluctuations have been found in the diamond chain [3][4][5], kagome-strip chains (KSCs) [6][7][8][9][10][11][12][13][14], and various frustrated one-dimensional chains [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33].…”