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 T-JT 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 < T-JT, the system of triplons may be in a liquid phase, which undergoes a transition into a superfluid phase at T <= T-c < T-JT. The dependence of the inversion temperature on the external magnetic field T-JT(H) has been calculated for quantum magnets of TlCuCl3 and Sr3Cr2O8.