Macroscopic Thermodynamical Witnesses of Quantum Entanglement
  We show that macroscopic thermodynamical properties - such as functions of internal energy and magnetization - can detect quantum entanglement in solids at nonzero temperatures in the thermodynamical limit. We identify the parameter regions (critical values of magnetic field and temperature) within which entanglement is witnessed by these thermodynamical quantities. 
Caslav Brukner and Vlatko Vedral