SPECTRA OF NON-HERMITIAN QUANTUM SPIN CHAINS DESCRIBING BOUNDARY INDUCED PHASE-TRANSITIONS

The spectrum of the non-Hermitian asymmetric XXZ-chain with additional nondiagonal boundary terms is studied. The lowest-lying eigenvalues a re determined numerically. For the ferromagnetic chain the temporal co rrelation length shows the same properties as the spatial correlation length. For the antiferromagnetic chain, we find a conformal invariant spectrum where the partition function corresponds to the one of a Cou lomb gas with only magnetic charges. This is in contrast to the case o f diagonal boundary terms where one finds only electric charges. Simil ar results are obtained in a toy model that can be diagonalized analyt ically in terms of free fermions.