Sufficient Condition for Entanglement Area Laws in Thermodynamically   Gapped Spin Systems
  We consider general locally-interacting arbitrary-dimensional lattice spin systems that are gapped for any system size. We show under reasonable conditions that nondegenerate ground states of such systems obey the entanglement area law. In so doing, we offer an intuitive picture on how a spectral gap restricts the correlations that a ground state can accommodate and leads to such a special feature. 
Jaeyoon Cho
quant-ph cond-mat.other