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 three-dimensional quantum rotors we derive explicit analytical formulae 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 and chemical potential). We find our results in overall qualitative agreement with basic thermodynamics of high-Tc cuprates.