Bipartite entanglements in spin-orbital systems

In this Letter we present the bipartite entanglement properties of the spin-orbital systems. After constructing the maximally entangled spin-orbital basis of bipartite, we find that the quantum entanglement length in the noninteracting itinerant electron system with spin and orbit degrees of freedom is considerably larger than that in the system with only spin. In SU(2)⊗SU(2) spin-orbital interacting system, the bipartite entanglement, expressed in terms of the spin-orbital correlation functions, clearly manifests the close relationship with the quantum phase in strongly correlated systems. The entanglement phase diagram of the finite-size systems is in agreement with the magnetic and orbital phase diagram of the infinite systems. The possible application of the present theory on nucleon systems is suggested.