Violation of the Zeroth Law of Thermodynamics in a spin chain.

A long-range interacting spin chain can exhibit temperature jump at the transition energy under the microcanonical description. After two identical long-range interacting subsystems of the same size at the same temperatures are weakly coupled, they exchange energy and the total microcanonical entropy of the full system increases irreversibly, leading to a violation of the Zeroth Law of Thermodynamics. In addition, microcanonical Monte Carlo simulations are performed to verify our conclusion. [ABSTRACT FROM AUTHOR]