First-order quantum phase transition in the orthogonal-dimer spin chain

Akihisa Koga, Kouichi Okunishi, Norio Kawakami
2000 Physical Review B (Condensed Matter)  
We investigate the low-energy properties of the orthogonal-dimer spin chain characterized by a frustrated dimer-plaquette structure. When the competing antiferromagnetic couplings are varied, the first-order quantum phase transition occurs between the dimer and the plaquette phases, which is accompanied by nontrivial features due to frustration: besides the discontinuity in the lowest excitation gap at the transition point, a sharp level-crossing occurs for the spectrum in the plaquette phase.
more » ... e further reveal that the plateau in the magnetization curve at 1/4 of the full moment dramatically changes its character in the vicinity of the critical point. It is argued that the first-order phase transition in this system captures some essential properties found in the two-dimensional orthogonal-dimer model proposed for SrCu_2(BO_3)_2.
doi:10.1103/physrevb.62.5558 fatcat:x6d6epxzmfgyzi4b6agzvot6xi