Phase Diagram of the spin S=1/2 Extended XY model
  The quantum phase transition in the ground state of the Extended spin S=1/2 XY model is studied in detail. Using the exact solution of the model the low temperature thermodynamics, as well as the ground state phase diagram of the model in the presence of applied uniform and/or staggered magnetic field are discussed. 
Irakli Titvinidze and G.I. Japaridze