von Neumann entropy spectra and entangled excitations in spin-orbital models

摘要

We consider the low-energy excitations of one-dimensional spin-orbital models which consist of spin waves, orbital waves, and joint spin-orbital excitations. Among the latter we identify strongly entangled spin-orbital bound states and spin-orbital quasiparticle states which appear as peaks in the von Neumann entropy spectral function introduced in this work. We present the scaling of the von Neumann entropy with system size and find a qualitatively different behavior for the bound state and the quasiparticle-the strong entanglement of these states is manifested by a universal logarithmic scaling of the von Neumann entropy with system size, while the entropy saturates for other spin-orbital excitations. We suggest that spin-orbital entanglement can be experimentally explored by the measurement of the dynamical spin-orbital correlations using resonant inelastic x-ray scattering, where strong spin-orbit coupling associated with the core hole plays a role.