A 2D quantum antiferromagnet with a four-fold degenerate valence-bond-solid ground state

Alain Gellé (1) , Andreas Läuchli (2) , Brijesh Kumar (3) , Frédéric Mila (1)

1 EPFL - Institut de théorie des phénomènes physiques
2 IRRMA - Institut Romand de Recherche Numérique en Physique des Matériaux
3 School of Physical Sciences

We study the competition between antiferromagnetic order and valence bond solid formation in a two-dimensional frustrated spin-1/2 model. The J1-J2 model on the square lattice is further frustrated by introducing products of three-spin projectors which stabilize four dimer-product states as degenerate ground states. These four states are reminiscent of the dimerized singlet ground state of the Shastry-Sutherland model. Using exact diagonalizations, we study the evolution of the ground state by varying theratio of interactions. For a large range of parameters (J2 > 0.25J1), our model shows a direct transition between the valence-bond-solid phase and the collinear antiferromagnetic phase. For small values of J2, several intermediate phases appear which are also analyzed.

Mots clés: Strongly Correlated Electrons; Spin Frustration; Low Dimensional Spin Systems

Domaines: Physique Quantique [quant-ph]; Electrons fortement corrélés [cond-mat.str-el]

Alain Gellé, Andreas Läuchli, Brijesh Kumar, Frédéric Mila. A 2D quantum antiferromagnet with a four-fold degenerate valence-bond-solid ground state. 2007. ⟨hal-00141909⟩