Spectral flow of non-hermitian Heisenberg spin chain with complex twist Original Research Article

We investigate the spectral flow of the integrable non-hermitian Heisenberg spin chain under boundary conditions with complex twist angle. It is shown that the period of the spectral flow is 4π up to a certain critical imaginary twist, beyond which the period jumps successively to higher values. We argue that this phenomenon caused by non-hermitian properties of the system is closely related to the metal-insulator transition caused by non-hermitian hoppings for the one-dimensional insulator.