Entanglement Entropy of the Low-Lying Excited States and Critical   Properties of an Exactly Solvable Two-Leg Spin Ladder with Three-Spin   Interactions
  In this work, we investigate an exactly solvable two-leg spin ladder with three-spin interactions. We obtain analytically the finite-size corrections of the low-lying energies and determine the central charge as well as the scaling dimensions. The model considered in this work has the same universality class of critical behavior of the XX chain with central charge c=1. By using the correlation matrix method, we also study the finite-size corrections of the Renyi entropy of the ground state and of the excited states. Our results are in agreement with the predictions of the conformal field theory. 
D. Eloy, J. C. Xavier
cond-mat.stat-mech cond-mat.str-el