Scaling of finite size effect of $α$-Rényi entropy in disjointed intervals under dilation

Abstract

The $α$-Rényi entropy in the gapless models have been obtained by the conformal field theory, which is exact in the thermodynamic limit. However, the calculation of its finite size effect (FSE) is challenging. So far only the FSE in a single interval in the XX model has been understood and the FSE in the other models and in the other conditions are totally unknown. Here we report the FSE of this entropy in disjointed intervals $A = \cup_i A_i$ under a uniform dilation $λA$ in the XY model, showing of a universal scaling law as \begin{equation*} Δ_{λA}^α= Δ_A^αλ^{-η} \mathcal{B}(A, λ), \end{equation*} where $|\mathcal{B}(A, λ)| \le 1$ is a bounded function and $η= \text{min}(2, 2/α)$ when $α< 10$. We verify this relation in the phase boundaries of the XY model, in which the different central charges correspond to the physics of free Fermion and free Boson models. We find that in the disjointed intervals, two FSEs, termed as extrinsic FSE and intrinsic FSE, are required to fully account for the FSE of the entropy. Physically, we find that only the edge modes of the correlation matrix localized at the open ends $\partial A$ have contribution to the total entropy and its FSE. Our results provide some incisive insight into the entanglement entropy in the many-body systems.