Strange metal solution of the Hubbard model

The numerically exact bold-line diagrammatic theory for the 2d Hubbard model exhibits a non-Fermi-liquid (NFL) strange metal state, which is connected to the SYK NFL in the strong-interaction limit. The solution for the doped system features the expected phenomenology with the NFL regime near half filling at strong couplings and in a wide temperature range enclosed by the atomic state at high temperatures and a Fermi liquid at low temperatures. However, the singularity structure of the diagrammatic series reveals that the solution in the half-filled and weakly doped regime corresponds to the unphysical branch of the Luttinger-Ward functional. On the other hand, our analysis suggests that in the optimally doped regime the characteristic NFL physics can be realized.