Essential singularity in the Renyi entanglement entropy of the one-dimensional XYZ spin-1/2 chain

Understand

We study the Renyi entropy of the one-dimensional XYZ spin-1/2 chain in the entirety of its phase diagram.

• The model has several quantum critical lines corresponding to rotated XXZ chains in their paramagnetic phase, and four tri-critical points where these phases join.
• Two of these points are described by a conformal field theory and close to them the entropy scales as the logarithm of its mass gap.
• The other two points are not conformal and the entropy has a peculiar singular behavior in their neighbors, characteristic of an essential singularity.