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Paper IPM / P / 11438  


Abstract:  
We have investigated the zero and finite temperature behaviors of the anisotropic
antiferromagnetic Heisenberg XXZ spin1/2 chain in the presence of a transverse
magnetic field (h).
The attention is concentrated on an interval of magnetic field between
the factorizing field (h_{f}) and the critical one (h_{c}).
The model presents a spinflop phase for 0 < h < h_{f} with an energy scale which
is defined by the long range antiferromagnetic order while it undergoes an
entanglement phase transition at h=h_{f}.
The entanglement estimators clearly show that the entanglement is lost
exactly at h=h_{f} which justifies different quantum correlations on both
sides of the factorizing field.
As a consequence of zero entanglement (at h=h_{f}) the ground state is known exactly
as a product of single particle states which is the starting point for initiating a spin wave
theory.
The linear spin wave theory is implemented to obtain the specific heat and thermal
entanglement of the model in the interested region.
A double peak structure is found in the specific heat around h=h_{f} which manifests
the existence of two energy scales in the system as a result of two competing orders
before the critical point.
These results are confirmed
by the low temperature Lanczos data which we have computed.
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