Exact solution of the open XXZ chain with general integrable boundary terms at roots ofunity

Abstract

We propose a Bethe-ansatz-type solution of the openspin-1/2 integrable XXZ quantum spin chain with general integrable boundary terms and bulk anisotropy valuesiπ/(p+1),where p is a positive integer. All six boundary parameters are arbitrary, andneed not satisfy any constraint. The solution is in terms of generalizedT–Q equations, havingmore than one Q function. We find numerical evidence that this solution gives the complete set of2N transfer matrixeigenvalues, where N is the number of spins.