Phase diagram of the Ashkin-Teller quantum spin chain

Abstract
We study a one-dimensional quantum Hamiltonian which is related to a highly anisotropic version of the two-dimensional Ashkin-Teller model. We explore the parameter region and complete its ground-state phase diagram. This problem is studied by using duality relations and by series expansions up to seventeenth order. Corresponding critical indices are also calculated. In this parameter region, a line of continuously varying critical indices is found.