Spin-1/2 anisotropic Heisenberg chain in longitudinal external magnetic field is studied by traditional Jordan-Wigner transformation and bosonization method. In the presence of an external field, both Fermi velocity and Fermi momentum are changed, thus the bosonization procedure is also changed. The antiferromagnetic phase and paramagnetic phase are discussed and the dependence of ground state energy and magnetization on the field are calculated and depicted for some typical cases.
Spin-1/2 anisotropic Heisenberg chain in longitudinal external magnetic field is studied by traditional Jordan-Wigner transformation and bosonization method. In the presence of an external field, both Fermi velocity and Fermi momentum are changed, thus the bosonization procedure is also changed. The antiferromagnetic phase and paramagnetic phase are discussed and the dependence of ground state energy and magnetization on the field are calculated and depicted for some typical cases.
One-dimensional spin-1-2 anisotropic Heisenberg antiferromagnet in a longitudinal external magnetic field is studied using bosonization method and Gaussian wave functional techniques which take account of the spatial structure.The magnetization and the energy of the ground state which depend on the external magnetic field are calculated.For the case of anisotropic parameter △＞△0,increasing of the external magnetic field above the threshold value leads to the appearance of the soliton lattice state in the ground state,until to an another critical field where the ground state changes to the canted state phase.Therefore,with increasing external magnetic field,the ground state experiences four different phases successively,namely,antiferromagnetic Ising,soliton lattice state canted state,and magnetization saturated phases.When △＜△0,the soliton lattice state phase does not appear,with increasing external field,the paramagnetic phase smoothly evolves into the canted state phase,finally reaches magnetization saturated phase.
Soliton Lattice State of Spin-21 Antiferromagnetic Chain in an External Magnetic Field
One-dimensional spin- anisotropic Heisenberg antiferromagnet in a longitudinal external magnetic field is studied using bosonization method and Gaussian wave functional techniques which take account of the spatial structure. The magnetization and the energy of the ground state which depend on the external magnetic field are calculated. For the case of anisotropic parameter , increasing of the external magnetic field above the threshold value leads to the appearance of the soliton lattice state in the ground state, until to an another critical field where the ground state changes to the canted state phase. Therefore, with increasing external magnetic field, the ground state experiences four different phases successively, namely, antiferromagnetic Ising, soliton lattice state canted state, and magnetization saturated phases. When , the soliton lattice state phase does not appear, with increasing external field, the paramagnetic phase smoothly evolves into the canted state phase, finally reaches magnetization saturated phase.
By using bosonization technique and Jordan-Wigner transformation,we study the spin(-1/2XY) model in external magnetic field.The bosonization procedure is changed in the presence of an external field.We study the model without external field firstly,and then the perturbation due to the external magnetic field is bosonized separately.We solve the incommensurability problem by redefining the bononic field operator,and correlation functions are calculated.Lastly,we talk simply about virtues of bosonization compared with other techniques.
The one-dimensional spin-1/2 XXZ model in a mixed transverse and longitudinal magnetic field is studied. Using the specially developed version of the mean-field approximation the order-disorder transition induced by the magnetic field is investigated. The ground-state phase diagram is obtained. The behavior of the model in the low transverse field is studied on the basis of conformal field theory. The relevance of our results to the observed phase transition in the quasi-one-dimensional antiferromagnet Cs2CoCl4 is discussed.
We present a variational approach to the Heisenberg antiferromagnetic model for spin 1/2 and anisotropic exchange, with an external longitudinal and transverse magnetic field. In the one-dimensional case, we calculate exactly with our trial function the expectation values of energy, sublattice magnetization, and magnetic susceptibility. On minimizing the energy, we obtain several phases, which depend on the strength of the field and anisotropy parameter. Subsequently we approach the problem numerically and solve it for a chain of 12 spins using the Lanczos method. The two approaches are in excellent concordance, particularly for the critical fields of the transitions, over a wide range of the parameters of the model. Beside its precision and mathematical simplicity, the method has the important advantage of accounting for the different magnetic phases and their transitions with a single trial function that has a compact mathematical expression. The formalism is expected to work better in higher dimensions, but the corresponding calculations are omitted because of the lack of numerical field-dependent data with which to compare.
In this work we study the Heisenberg XXZ antiferromagnetic model for spin S and dimension d in the presence of an external longitudinal magnetic field. First, we essay a variational approach which uses as trial function a version of the analytic expression for the ground state given by the paired nonmagnetic excitation (PNME) theory [M. Lagos and G. G. Cabrera, Solid State Commun. 67, 221 (1988); Phys. Rev. B 38, 659 (1988)], generalized in order to incorporate the external field. The ground-state energy, sublattice magnetization, and magnetic susceptibility are obtained. Subsequently, we solve the problem numerically for a chain of 12 spins (S=1 and S=3/2) using the Lancz\"os method [E. Dagotto and A. Moreo, Phys. Rev. D 31, 865 (1985)]. The two approaches give excellent concordance over a wide range of the parameters of the model. We show that our analytic trial function represents accurately the ground state of the system for anisotropies ranging from the Ising limit to the almost isotropic Heisenberg model for all values of the field. Moreover, it accounts for the several antiferromagnetic and ferromagnetic phases occurring for different values of the magnetic field with the same precision. The critical fields of the transitions are predicted correctly. Also, results for various spin values S in two and three dimensions are presented.