Impact of a Lifshitz transition on the onset of spontaneous coherence

Lifshitz transitions are topological transitions of a Fermi surface, whose signatures typically appear in the conduction properties of a host metal. Here, we demonstrate, using an extended Falicov-Kimball model of a two-flavor fermion system, that a Lifshitz transition which occurs in the noninteracting limit impacts interaction-induced insulating phases, even though they do not host Fermi surfaces. For strong interactions we find a first-order transition between states of different polarization. This transition line ends in a very unusual quantum critical endpoint, whose presence is stabilized by the onset of interflavor coherence. We demonstrate that the surfaces of maximum coherence in these states reflect the distinct Fermi-surface topologies of the states separated by the noninteracting Lifshitz transition. Experimental realizations of our results are discussed for both electronic and optical lattice systems.