arXiv:1503.01094 · Physical Review B
Universal logarithmic corrections to entanglement entropies in two dimensions with spontaneously broken continuous symmetries
David J. Luitz, Xavier Plat, Fabien Alet, Nicolas Laflorencie
Abstract
We explore the R\'enyi entanglement entropies of a one-dimensional (line) subsystem of length $L$ embedded in a two-dimensional $L\ifmmode\times\else\texttimes\fi{}L$ square lattice for quantum spin models whose ground state breaks a continuous symmetry in the thermodynamic limit. We first study the ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ Heisenberg model (with antiferromagnetic nearest-neighbor ${J}_{1}>0$ and ferromagnetic second-neighbor couplings ${J}_{2}\ensuremath{\le}0)$, breaking SU(2) symmetry in the ground state, using quantum Monte Carlo simulations. The signature of SU(2)-symmetry breaking on finite-size systems, ranging from $L=4$ up to $L=40$, clearly appears as a universal additive logarithmic correction to the R\'enyi entanglement entropies: ${l}_{q}lnL$ with ${l}_{q}\ensuremath{\simeq}1$, independent of the R\'enyi index and values of ${J}_{2}$. We then confirm this result using a spin-wave analysis (with restored spin rotational symmetry) on the same ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ model, as well as on the XY model, with a $U(1)$ broken symmetry in the ground state. The high-precision spin-wave calculations are performed on finite lattices up to ${10}^{5}\ifmmode\times\else\texttimes\fi{}{10}^{5}$ sites, allowing us to explore further nonuniversal finite-size corrections. Our results fully agree with the prediction ${l}_{q}={n}_{G}/2$, where ${n}_{G}$ is the number of Goldstone modes, by Metlitski and Grover (arXiv:1112.5166).