Thermodynamic behavior of the XXZ Heisenbergs = 1/2 chain around the factorizing magnetic field

Abstract

We have investigated the zero-and finite-temperature behaviorsof the anisotropic antiferromagnetic Heisenberg XXZ spin-1/2 chain in the presence of a transverse magnetic field (h). The attention is concentrated on an interval of magnetic field between the factorizing field (hf) and the critical one (hc). The model presents aspin-flop phase for 0 < h < hf with an energy scale which is defined by the long range antiferromagneticorder while it undergoes an entanglement phase transition ath = hf. The entanglement estimators clearly show that the entanglement is lost exactly ath = hf, which justifies different quantum correlations on both sides ofthe factorizing field. As a consequence of zero entanglement (ath = hf) the ground state is known exactly as a product of single-particle states which is thestarting point for initiating a spin wave theory. The linear spin wave theory isimplemented to obtain the specific heat and thermal entanglement of the model in theinterested region. A double-peak structure is found in the specific heat aroundh = hf, which manifests the existence of two energy scales in the system as a result of twocompeting orders before the critical point. These results are confirmed by the lowtemperature Lanczos data which we have computed.