I was always curios what real material are described by the fermionic Hubbard model.
$$H = \sum_{\left< i, j\right> \sigma} t_{ij} c^{\dagger}_{i, \sigma} c_{j, \sigma} + \sum_i U_i n_{i\uparrow} n_{\downarrow} + \sum_{i\sigma} \mu_{i \sigma} n_{i \sigma}$$
It has been popular for years, but, I guess, because it is simplest quantum model that has insulating and conducting properties at different limits. ($t = 0$ for insulating, $U = 0$ for conducting) with non trivial interplay in some intermediate state. Plus it predicts Mott insulating phase.
It is nice that it can be solved in 1 dimension, in the $t=0$ and $U=0$ limits and serve in solid state physics as Ising model in statistical physics.
But how is it related to the real life?
I know only about square lattice describing $CuO_2$ plane in cuprates and cold atom experiments.
Are there any other materials that can be described with it?