Sahoo Shaon, Durga Prasad Goli V M L, Sen Diptiman, Ramasesha S
Solid State & Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India.
J Phys Condens Matter. 2014 Jul 9;26(27):276002. doi: 10.1088/0953-8984/26/27/276002. Epub 2014 Jun 17.
We study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic (J(F)(1)) and antiferromagnetic (J(A)(1)) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction (J(F)(2)). In this model frustration is present due to the non-zero J(F)(2). The model with site spin s behaves like a Haldane spin chain, with site spin 2s in the limit of vanishing J(F)(2)and large J(F)(1)/J(A)(1). We show that the exact ground state of the model can be found along a line in the parameter space. For fixed J(F)(1), the phase diagram in the space of J(A)(1)-J(F)(2) is determined using numerical techniques complemented by analytical calculations. A number of quantities, including the structure factor, energy gap, entanglement entropy and zero temperature magnetization, are studied to understand the complete phase diagram. An interesting and potentially important feature of this model is that it can exhibit a macroscopic magnetization jump in the presence of a magnetic field; we study this using an effective Hamiltonian.
我们研究了具有交替铁磁（(J(F)(1))）和反铁磁（(J(A)(1))）最近邻相互作用以及铁磁次近邻相互作用（(J(F)(2))）的海森堡自旋 - 1/2 和自旋 - 1 链。在该模型中，由于非零的(J(F)(2))存在阻挫。具有格点自旋(s)的模型在(J(F)(2))消失且(J(F)(1)/J(A)(1))很大的极限下，表现得像一个霍尔丹自旋链，此时格点自旋为(2s)。我们表明，该模型的精确基态可以在参数空间中的一条线上找到。对于固定的(J(F)(1))，利用数值技术并辅以解析计算来确定(J(A)(1) - J(F)(2))空间中的相图。研究了包括结构因子、能隙、纠缠熵和零温磁化强度在内的一些量，以理解完整的相图。该模型一个有趣且可能重要的特征是，在磁场存在时它可以表现出宏观磁化强度跳跃；我们使用有效哈密顿量对此进行了研究。
