Wigner Function of Thermo-Invariant Coherent State

By using the thermal Winger operator of thermo-field dynamics in the coherent thermal state |ξ> representation and the technique of integration within an ordered product of operators, the Wigner function of the thermo-invariant coherent state |z, N>is derived. The nonclassical properties of state |z, N> is discussed based on the negativity of the Wigner function.