Nontransverse factorizing fields and entanglement in finite spin systems

M. CEREZO; R. ROSSIGNOLI; N. CANOSA

PHYSICAL REVIEW B - SOLID STATE

American Physical Society

Lugar: New York; Año: 2015 vol. 92 p. 224221 - 224229

0556-2805

We determine the conditions for the existence of nontransverse factorizing magnetic fields in general spin arrays with anisotropic XYZ couplings of arbitrary range. It is first shown that a uniform, maximally aligned,completely separable eigenstate can exist just for fields hs parallel to a principal plane and forming four straight lines in the field space, with the alignment direction different from that of hs and determined by the anisotropy.Such a state always becomes a nondegenerate ground state for sufficiently strong (yet finite) fields along these lines, in both ferromagnetic and antiferromagnetic-type systems. In antiferromagnetic chains, this field coexistswith the nontransverse factorizing field hs associated with a degenerate N´eel-type separable ground state, which is shown to arise at a level crossing in a finite chain. It is also demonstrated for arbitrary spin that pairwiseentanglement reaches full range in the vicinity of both hs and hs , vanishing at hs but approaching small yet finite side limits at hs , which are analytically determined. The behavior of the block entropy and entanglement spectrum in their vicinity is also analyzed.