Statistical Thermodynamics of the Fr\"ohlich-Bose-Einstein Condensation of Magnons out of Equilibrium

Phys. Rev. E 100, 032126 (2019) A non-equilibrium statistical-thermodynamic approach to the study of a Fr\"ohlich-Bose-Einstein condensation of magnons under radio-frequency radiation pumping is presented. Such a system displays a complex behavior consisting in steady-state conditions to the emergence of a synergetic dissipative structure resembling the Bose-Einstein condensation of systems in equilibium. A kind of "two fluid model" arises: the "normal" non-equilibrium structure and Fr\"ohlich condensate or "non-equilibrium" one, which is shown to be an attractor to the system. We analyze some aspects of the irreversible thermodynamics of this dissipative complex system, namely, its informational entropy, expressions for the fluctuations in non-equilibrium conditions, the associated Maxwell relations and the formulation of a generalized $\mathscr{H}$-theorem. We also study the informational entropy production of the system, an order parameter is introduced and Glansdorff-Prigogine criteria for evolution and (in)stability are verified.