Abstract
We present a sign-problem free quantum Monte Carlo study of a model that exhibits quantum phase transitions without symmetry breaking and associated changes in the size of the Fermi surface. The model is an Ising gauge theory on the square lattice coupled to an Ising matter field and spinful `orthogonal' fermions at half-filling, both carrying Ising gauge charges. In contrast to previous studies, our model hosts an electron-like, gauge-neutral fermion excitation providing access to Fermi liquid phases. One of the phases of the model is a previously studied orthogonal semi-metal, which has $\mathbb{Z}_2$ topological order, and Luttinger-volume violating Fermi points with gapless orthogonal fermion excitations. We elucidate the global phase diagram of the model: along with a conventional Fermi liquid phase with a large Luttinger-volume Fermi surface, we also find a `deconfined' Fermi liquid in which the large Fermi surface co-exists with fractionalized excitations. We present results for the electron spectral function, showing its evolution from the orthogonal semi-metal with a spectral weight near momenta $\{\pm \pi/2, \pm \pi/2\}$, to a large Fermi surface.
Highlights
Quantum phase transitions involving a change in the volume enclosed by the Fermi surface play a fundamental role in correlated electron compounds
Such approaches focus on density wave ordering transitions [14,15,16,17,18,19,20,21,22,23,24,25,26,27], where spontaneous translational symmetry breaking accompanies the change in the Fermi volume: both sides of the transition have a Luttinger-volume Fermi surface, after the expansion of the unit cell by the density wave ordering is taken into account
As we turn up the attractive force between the fα fermions and the Ising matter (Higgs) field τz, we find a transition from the orthogonal semimetal (OSM) to a phase with a large Luttinger-volume Fermi surface of the cα but with the Z2 gauge sector remaining deconfined
Summary
Quantum phase transitions involving a change in the volume enclosed by the Fermi surface play a fundamental role in correlated electron compounds. As we turn up the attractive force between the fα fermions and the Ising matter (Higgs) field τz, we find a transition from the OSM to a phase with a large Luttinger-volume Fermi surface of the cα but with the Z2 gauge sector remaining deconfined Such a phase does not contradict the topological arguments, which do not require (but do allow) a Luttinger-violating. We note the recent study of Chen et al [37], which examines a Z2 gauge theory coupled to orthogonal fermions fα and an Ising matter field τz Their Z2-deconfined phase is different from ours and earlier studies [31,32]: Their phase has a large, Luttinger-volume Fermi surface of the fα fermions, which move in a background of zero flux V, we summarize our results, discuss relations to experiments, and highlight future directions
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