Effects of edges in spin-12 bond-alternating Heisenberg chains: matrix-product variational approach

Abstract

We make a matrix-product variational approach to spin-1 2 ferromagnetic-antiferromagnetic bondalternating chains with anisotropy on their ferromagnetic bonds, especially under the open boundary condition. The rich phase diagram containing the Haldane, large-D, and two types of Néel phases is well reproduced with only two variational parameters. The on-bond anisotropy has a significant effect on the ferromagnetic coupling between neighboring spins and induces novel edge states peculiar to spin-1 2 chains.

Fermionic versus bosonic descriptions of one-dimensional spin-gapped antiferromagnets

“…On the other hand, the thermodynamic properties have much less been calculated so far 87,94 and there is no guiding theory for extensive experimental findings. Employing two different languages, we calculate various thermal quantities and give rigorous information on their lowtemperature behavior.…”

“…74 These materials behave as spin-1 Haldane-gap antiferromagnets at low temperatures, 75,76,77,78 while such spin-1 features are broken up into paramagnetic spin 1 2 's with increasing temperature. 79,80,81 Besides the thermal crossover from quantum spin 1's to classical spin 1 2 's, their enriched ground-state properties 82,83,84,85,86 and novel edge states 87 are of great interest to both theoreticians and experimentalists.…”