Thermodynamic properties of the SO(5) model of high-Tc superconductivity
  In this paper we present calculations of thermodynamic functions within Zhang's SO(5) quantum rotor theory of high-Tc superconductivity. Using the spherical approach for the three-dimensional quantum rotors we derieved explicit analytical formulas for entropy and specific heat related to the lattice version of the SO(5) nonlinear quantum-sigma model. We present the temperature dependence of these quantities for various settings of relevant control parameters (quantum fluctuations, chemical potential). We find our results in overal qualitative agreement with basic thermodynamics of high-Tc cuprates. 
T. A. Zaleski and T. K. Kopec