Investigation entanglemenet entropy and entanglement spectrum of the spin-1/2 chain with hexamer modulation of exchange

In this paper, we consider the spin-1/2 Heisenberg chain with alternating exchange in presence of hexamer modulation of exchange on bonds. We studied the effect of uniform external magnetic field on the ground state phase diagram of this model using numerical Lanczos method. The ground state phase diagram consists of three gapless Luttinger Liquid(LL), two gapped plateau phases and a singlet spin phase. It is specified in the presence of additional modulation of exchange, the magnetization curve of system has two plateaus in magnetization diagram that are equal to and of the saturation value, respectively. Here, numerically we compute the entanglement entropy and the entanglement spectrum for a chain with finite number of particle. Numerical results shows that the singlet gapped phase exhibits four times degenerate and the first and second gapped plateau phases indicate two times degenerate.