Ground-State Properties of s=1 Easy-Plane Ferromagnetic Heisenberg Chains

Lihua Pan, Yu Cao, Bin Xi +1 more

Andrei A. Zvyagin, V. M. Tsukernik

Alvaro Caramico D’Auria, L. De Cesare, Maria Teresa Mercaldo +1 more

Hiroshi Ueda, Shigeki Onoda

The spin-$1/2$ Heisenberg chain with a ferromagnetic first-neighbor exchange coupling ${J}_{1}$ and an antiferromagnetic second-neighbor ${J}_{2}$ has a Haldane dimer ground state with an extremely small spin gap. Thus the ground state is readily altered by perturbations. Here, we investigate the effects of XXZ exchange magnetic anisotropy of both the easy-axis and easy-plane types and an alternation in ${J}_{1}$ on the ground state, the spin gap, and magnetic properties of the frustrated ferromagnetic spin-$1/2$ chain. It is found that there are two distinct dimerized spin-gap phases, in one of which the spin gap and the magnetic susceptibility are extremely small around the SU(2) symmetric case and in the other they are moderately large far away from the SU(2) symmetric case. A small alternation in the amplitude of ${J}_{1}$ rapidly shortens the pitch of spin correlations towards the four-spin periodicity, as in the limit of ${J}_{1}/{J}_{2}\ensuremath{\rightarrow}0$. These effects are not sufficient to quantitatively explain overall experimentally observed magnetic properties in the quasi-one-dimensional spin-gapped magnetoelectric cuprate ${\mathrm{Rb}}_{2}{\mathrm{Cu}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{12}$ that exhibits ferroelectricity stabilized by a magnetic field. Our results are also relevant to ${\mathrm{Cs}}_{2}{\mathrm{Cu}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{12}$, where the ferromagnetic intrachain and antiferromagnetic interchain order has recently been found, in a single chain level. We also reveal the nature of symmetry-protected topological phase transitions in the model by mapping onto effective spin-1 chain models.

Adriana Moreo

Bing Tang, Dejun Li

The existence and properties of quantum breathers in a one-dimensional XXZ ferromagnetic Heisenberg spin chain with single-ion easy-plane anisotropy are investigated analytically in the Hartree approximation. We show that the system can support the appearance of quantum breathers, and discuss their existence conditions and properties. In addition, our results show that, for quantum breathers in this system, both the corresponding energy and magnetic moment are quantized.