Sahoo Shaon, Dey Dayasindhu, Saha Sudip Kumar, Kumar Manoranjan
S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
Department of Physics, Indian Institute of Technology Tirupati, Tirupati 517506, India.
J Phys Condens Matter. 2020 May 15;32(33). doi: 10.1088/1361-648X/ab8663.
A Heisenberg spin-chain with alternating ferromagnetic (FM) (-J1F<0) and antiferromagnetic (J1A>0) nearest-neighbor (NN) interactions, exhibits the dimer and spin-2Haldane phases in the limitsJ1F/J1A→0andJ1F/J1A→∞respectively. These two phases are understood to be topologically equivalent. Induction of the frustration through the next NN FM interaction (-J2F<0) produces a very rich quantum phase diagram. With frustration, the whole phase diagram is divided into a FM and a nonmagnetic (NM) phase. For= 1/2, the full NM phase is seen to be of Haldane-dimer type, but for> 1/2, a spiral phase comes between the FM and the Haldane-dimer phases. The study of a suitably defined string-order parameter and spin-gap at the phase boundary indicates that the Haldane-dimer and spiral phases have different topological characters. We also find that, along theJ2F=12J1Fline in the NM phase, an NN dimer state is thegroundstate, providedJ1A>JC=κJ1Fwhere⩽+for applied magnetic field. Without magnetic field, the position ofis on the FM-NM phase boundary when= 1/2, but for> 1/2, the location ofis on the phase separation line between the Haldane-dimer and spiral phases.
一个具有交替铁磁（FM）（-J1F<0）和反铁磁（J1A>0）最近邻（NN）相互作用的海森堡自旋链，分别在J1F/J1A→0和J1F/J1A→∞的极限情况下呈现出二聚体和自旋 - 2霍尔丹相。这两个相被认为在拓扑上是等价的。通过次近邻FM相互作用（-J2F<0）引入的失谐产生了一个非常丰富的量子相图。有了失谐，整个相图被分为一个铁磁相和一个非磁（NM）相。对于= 1/2，整个非磁相被认为是霍尔丹 - 二聚体类型，但对于> 1/2，在铁磁相和霍尔丹 - 二聚体相之间会出现一个螺旋相。对相边界处适当定义的弦序参量和自旋能隙的研究表明，霍尔丹 - 二聚体相和螺旋相具有不同的拓扑特征。我们还发现，在非磁相中的J2F = 12J1F线上，只要J1A>JC = κJ1F（其中对于外加磁场⩽ +），NN二聚体态就是基态。没有磁场时，当= 1/2时处于铁磁 - 非磁相边界，而对于> 1/2，处于霍尔丹 - 二聚体相和螺旋相之间的相分离线上。
