2001/04/30 by T. Sommer, Torsten Sommer, Matthias Vojta +3 · 83 citations
Physics and Astronomy · #Advanced Condensed Matter Physics #Antiferromagnetism #Ferromagnetism #Ground state #Magnetic field #Physics of Superconductivity and Magnetism #Singlet state #Spin (aerodynamics) #Spin wave #Spins #Square lattice #Topological Materials and Phenomena #cond-mat.mes-hall #cond-mat.str-el
paper · pdf · doi:10.1007/s100510170052
published in The European Physical Journal B 23(3), 329-339 (Springer Science+Business Media) · 12 pages, 9 figs; added references; final version as published
openalex publication_date 2001/10/01 · arxiv created 2001/11/02 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The two-layer square lattice quantum antiferromagnet with spins 1/2 shows a zero-field magnetic order-disorder transition at a critical ratio of the inter-plane to intra-plane couplings. Adding a uniform magnetic field tunes the system to canted antiferromagnetism and eventually to a fully polarized state; similar behavior occurs for ferromagnetic intra-plane coupling. Based on a bond operator spin representation, we propose an approximate ground state wavefunction which covers all phases by means of a unitary transformation. The excitations can be efficiently described as independent bosons; in the antiferromagnetic phase these reduce to the well-known spin waves, whereas they describe gapped spin-1 excitations in the singlet phase. We compute the spectra of these excitations as well as the magnetizations throughout the whole phase diagram.