1/r 2 t-J Model in a Magnetic Field

Minoru Takahashi

Jin‐Ming Liu, Pengfei Yu, Ji-Guang Cai +1 more

We investigate the thermal entanglement of a two-qubit anisotropic Heisenberg XYZ model with both uniform and nonuniform magnetic fields in the x-z plane at thermal equilibrium. For the uniform magnetic field case, it is shown that the value of the critical magnetic field B(subscript c) may be broadened by changing the direction of the magnetic field and that the revival of entanglement is due to the combined influence of the magnetic field and the Heisenberg model's partial anisotropy in the plane which is perpendicular to the magnetic field. Moreover, the direction of the magnetic field will have an effect on the critical temperature T(subscript c) only when the field strength is large enough. For the nonuniform magnetic field case it is found that, for any direction of the magnetic field, the introduction of inhomogeneity in the magnetic field always broadens the critical magnetic field B(subscript c), but diminishes the maximum entanglement.

Hamid Arian Zad, Moones Sabeti, Azam Zoshki

Magnetic and thermodynamic properties of the anisotropic Heisenberg XXZ spin=1/2 chain under both homogeneous and inhomogeneous magnetic fields are theoretically studied at finite low temperature. To this end, we rigorously study the magnetization, magnetic susceptibility and specific heat of the model in the vicinity of three different magnetic fields including longitudinal, transverse and transverse staggered magnetic fields. The thermodynamic parameters of the model are investigated under two conditions separately: I) when the model is putted in the presence of homogeneous magnetic fields; II) when a finite inhomogeneity is considered for all applied magnetic fields in the Hamiltonian. We show that at low temperature, independent of the chain size, the magnetization curve versus longitudinal field has some plateaus, which convert to their counterpart quasi-plateaus when the transverse magnetic field increases. Moreover, the influence of the transverse and staggered transverse magnetic fields, and their corresponding inhomogeneities on the magnetization, susceptibility, and specific heat is reported in detail. We find that the inhomogeneity has a substantial effect on the thermodynamic parameters of the model under consideration.

Yuta Saiga, Mitsuhiro Arikawa, T Yamamoto +1 more

M Ghasemloo, N Nikdel, Mohammad Reza Soltani +2 more

In this paper we studied the thermal negativity in a two-qubit XX spin ½ chain model and XXX spin 1/2 chain model(isotropic Heisenberg model)spin-1/2 chain subjected to an external magnetic field in z direction. We calculate analytical relation for the thermal negativity for two qubit XX and XXX spin chain models in the external magnetic field. Effects of the magnetic field and temperature on the negativity are shown. We have also plotted two kind of behavior in the thermal negativity which scales by magnetic field and temperature. It is shown that when the magnetic field along in axis z is considerable, thermal negativity can be decrease for higher temperature. We found the critical temperature of negativity for XX spin chain model and XXX spin chain model with added external magnetic field where there are independent from magnetic field. We also have shown in both of two models after T=TC the negativity is zero. We find the critical temperature for this models and show that the critical temperature is independent of magnetic field. We found that the negativity with increasing the temperature T, at first the quantum correlations in the system increase, smoothly reaches the maximum, and then after the critical temperature turn into zero.