R. Cuerno et A. Gonzalezruiz, FREE FERMIONIC ELLIPTIC REFLECTION MATRICES AND QUANTUM GROUP INVARIANCE, Journal of physics. A, mathematical and general, 26(14), 1993, pp. 605-610
Diagonal solutions for the reflection matrices associated to the ellip
tic R matrix of the eight-vertex free fermion model are presented. The
y lead through the second derivative of the open chain transfer matrix
to an XY Hamiltonian in a magnetic field which is invariant under a q
uantum deformed Clifford-Hopf algebra,