Fermi-surface reconstruction without symmetry breaking

摘要: We present a sign-problem free quantum Monte Carlo study of model, which exhibits phase transitions without symmetry breaking, along with associated changes in the size Fermi surface. The model is an Ising gauge theory on square lattice coupled to matter field and spinful `orthogonal' fermions at half-filling, both carrying charges. In contrast previous studies, our hosts electron-like, gauge-neutral fermion excitation providing access liquid phases. One phases previously studied orthogonal semi-metal, has $\mathbb{Z}_2$ topological order, Luttinger-volume violating points gapless excitations. elucidate global diagram also contains confining liquid, large results for electron spectral function, showing its evolution from semi-metal weight near momenta $\{\pm \pi/2, \pm \pi/2\}$,