Baxter Q-operator and functional relations

We obtain the Baxter Q-operators in the U-q (sl(2)) over cap invariant integrable models as a special limits of the quantum transfer matrices corresponding to different spins in the auxiliary space. We derive the Baxter equation from the well-knownfusion relations for the transfer matrices. Our method is valid for an arbitrary integrable model corresponding to the quantum group U-q (sl(2)) double under bar, for example for the XXZ-spin chain. (C) 2015 The Author. Published by Elsevier B.V.