New indicators of quantum phase transitions in several condensed-matter systems

By analyzing parameter-dependence of the linear entropy and the negativity of a block of L/2 odd-number spins, we study quantum phase transitions (QPTs) in the spin-1/2 Heisenberg XXZ model, the dimerized Heisenberg model, the dimerized-frustrated Heisenberg model and the spin-1 quadratic–biquadratic Heisenberg model. The numerical results reveal that most of the QPTs can be detected exactly by discontinuities, singularities or extreme points of these two quantities with finite-size samples. This fact implies that the linear entropy and the negativity can serve as efficient indicators of QPTs occurring in a variety of condensed-matter systems.