G. Albertini et al., PHASE-DIAGRAM OF THE NON-HERMITIAN ASYMMETRIC XXZ SPIN CHAIN, Journal of physics. A, mathematical and general, 29(15), 1996, pp. 369-376
The low-lying excitations of the asymmetric XXZ spin chain are derived
explicitly in the antiferromagnetic regime through the Bethe ansatz.
It is found that a massless and conformal invariant phase with central
charge c = 1 is separated from a massive phase by a line on which the
low-lying excitations surprisingly scale with the lattice length as D
elta E similar to N--1/2. The mass gap vanishes with an exponent 1/2 a
s one approaches the massless phase. The connection with the asymmetri
c six-vertex model and some physical consequences are discussed.