Characteristic temperatures of a triplon system of dimerized quantum magnets

Exploiting the analogy between ultracold atomic gases and the system of triplons, we study magneto-thermodynamic properties of dimerized quantum magnets in the framework of Bose–Einstein condensation (BEC). Particularly, introducing the inversion (or Joule–Thomson) temperature TJT as the point where Joule–Thomson coefficient of an isenthalpic process changes its sign, we show that for a simple paramagnet, this temperature is infinite, while for three-dimensional (3D) dimerized quantum magnets it is finite and always larger than the critical temperature Tc of BEC. Below the inversion temperature T<TJT, the system of triplons may be in a liquid phase, which undergoes a transition into a superfluid phase at T≤Tc<TJT. The dependence of the inversion temperature on the external magnetic field TJT(H) has been calculated for quantum magnets of TlCuCl3 and Sr3Cr2O8.