Exactly solvable frustrated quantum spin models consisting of a diamond unit structure are presented. The ground states are characterized by tetramer-dimer states with a macroscopic degeneracy in a certain range of isotropic exchange interaction. The lower bound of the excitation gap is exactly calculated to be finite, and the bulk entropy in the limit of zero temperature remains finite depending on the shape of the boundary of the system. Residual entropy is in the range of 0-6.1% of the entropy at high temperature for a hexagonal diamond lattice and 0-8.4% for a square diamond lattice. These diamond spin lattices are generalized to any dimensions and some of them are likely to be synthesized experimentally.
ASJC Scopus subject areas
- Physics and Astronomy(all)