title: Entanglement, subsystem particle numbers and topology in free fermion systems.
abstract: We study the relationship between bipartite entanglement, subsystem particle number and topology in a half-filled free fermion system. It is proposed that the spin-projected particle numbers can distinguish the quantum spin Hall state from other states, and can be used to establish a new topological index for the system. Furthermore, we apply the new topological invariant to a disordered system and show that a topological phase transition occurs when the disorder strength is increased beyond a critical value. It is also shown that the subsystem particle number fluctuation displays behavior very similar to that of the entanglement entropy. This provides a lower-bound estimation for the entanglement entropy, which can be utilized to obtain an estimate of the entanglement entropy experimentally.
authors.affiliation: National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China.
authors.forename: Y F
authors.initials: YF
authors.lastname: Zhang
authors.forename: L
authors.initials: L
authors.lastname: Sheng
authors.forename: R
authors.initials: R
authors.lastname: Shen
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: D Y
authors.initials: DY
authors.lastname: Xing
mesh_terms: D003198:Computer Simulation; D004601:Elementary Particles; D008956:Models, Chemical; D010316:Particle Size; D011789:Quantum Theory; D013113:Spin Labels
chemical_list: D013113:Spin Labels