Metaplectic Iwahori Whittaker functions and supersymmetric lattice models

In this paper we consider Iwahori Whittaker functions on $n$-fold metaplectic covers $widetilde{G}$ of $mathbf{G}(F)$ with $mathbf{G}$ a split reductive group over a non-archimedean local field $F$. For every element $phi$ of a basis of Iwahori Whittaker functions, and for every $ginwidetilde{G}$, we evaluate $phi(g)$ by recurrence relations over the Weyl group using vector Demazure-Whittaker operators. Specializing to the case of $mathbf{G} = mathbf{GL}_r$, we exhibit a solvable lattice model whose partition function equals $phi(g)$. These models are of a new type associated with the quantum affine super group $U_q(widehat{mathfrak{gl}}(r|n))$. The recurrence relations on the representation theory side then correspond to solutions to Yang-Baxter equations for the lattice models. Remarkably, there is a bijection between the boundary data specifying the partition function and the data determining all values of the Whittaker functions.