Jahn–Teller effect and adiabatic cooling in the vicinity of crossover point

• At T=0, level spacing δ does not change all over the domain of existence of JT effect.
• It is also true for the states minimizing internal energy at an isothermal process.
• Entropy depends only on T and on δ/T and thus adiabatic process is isothermal as well.

It is shown that an ensemble of two-state systems, which commonly works as a refrigerator when the levels adiabatically approach each other, turns into a thermostat as soon as the Jahn–Teller effect emerges.