Nature of disordered phase of the frustrated spin-1/2 Ising-Heisenberg model on martini lattices
Department of Theoretical Physics and Astrophysics, Institute of Physics, UPJŠ
In this work, we have exactly solved the spin-1/2 Ising-Heisenberg model on two new geometrically related martini lattices using the generalized star-triangle transformation which establishes an exact mapping relationship to the effective spin-1/2 Ising model on a triangular lattice. The investigated quantum spin models exhibit in the ground-state phase diagram three different phases: the classical ferromagnetic phase, the quantum ferromagnetic and a quantum disordered phases. In opposite to the classical ferromagnetic long-range ordering spontaneous magnetization of Heisenberg and Ising spins show within the long-range ordered quantum ferromagnetic phase a quantum reduction. The classical and quantum ferromagnetic phases coexist together with the quantum disordered phase at an intriguing triple point around which one observes anomalous magnetic and thermodynamic behaviors. It is evidenced that the spontaneous magnetizations and the logarithmic divergence of the specific heat disappear within the parameter regions corresponding to the disordered quantum phase.