I have in mind the transverse ising model and its (self-dual) generalizations, such as
$$H_{TI} = \sum_i \sigma^z_{i}\sigma^z_{i+1} + h \sigma^x_{i}$$ and $$H_{SDANNI} = \sum_i (\sigma^z_{i}\sigma^z_{i+1}+\Delta \sigma^z_{i}\sigma^z_{i+2}) + h( \sigma^x_{i}+\Delta \sigma^x_{i}\sigma^x_{i+1})$$
These models are self-dual under a Kramers-Wannier mapping, which is often used to show that $h=1$ is the location of the critical point. There are often some subtleties with this transformation to do with the tails of the mapping and the degeneracy of ground states.
At the critical point of $h=1$, does there exist a unitary $U$ implementing the duality such that $U H_{TI} U^\dagger = H_{TI}$ and $U H_{SDANNI} U^\dagger = H_{SDANNI}$?
My motivation to ask this is fairly vague. I keep feeling that these models have an extra symmetry at the critical point of $h=1$ relative to their $h\neq 1$ counterparts, and I suspect it is related to the fact that they are dual to themselves at the critical point. In particular, I want to implement this symmetry in exact diagonalization. My mind says that it's unlikely one can find a unitary operator (or even any linear operator) to implement Kramers-Wannier duality, but my heart hopes that it exists and it's known.