The q-deformed Haldane-Shastry chain at q=i with even length

Abstract

In this note we announce some results extending our recent work with A. Toufik on the free-fermion point q=i of the Haldane-Shastry chain to the case with an even number N of sites. The resulting long-range version of the Heisenberg XX chain may be viewed as a model of fermions with extended gl(1|1) symmetry. Unlike for odd N, the conserved charges are nilpotent and exhibit Jordan blocks.