Résumé |
Gauge theories play a central role in the theoretical description of unconventional
phases of matter that go beyond the standard paradigms of quantum statistical
mechanics. While in high-energy physics, gauge fields correspond to fundamental
particles, in condensed matter theory they are typically emergent and are invoked
as an effective description of the low-energy degrees of freedom. Notable examples
include spin-liquids, doped Mott insulators, and the fractional Hall effect, among
others. In my talk, I will present a sign-problem free quantum Monte Carlo study of
a lattice model hosting 'orthogonal' fermions coupled to an Ising-Higgs gauge
theory. Our model provides a simple yet highly non-trivial example of electron
fractionalization, which, crucially, remains numerically tractable. We uncover a
particularly rich phase diagram arising from strong correlations between gauge and
matter fields. In particular, we find that in the background of pi-flux lattice an
orthogonal semi-metal (OSM) forms with gapless Dirac fermion excitations. With the
tuning of parameters, the OSM undergoes a confinement transition, in which symmetry
breaking and confinement are coincident. We construct a field-theoretical
description of the transition involving condensation of a matrix Higgs field. The
critical theory is predicted to sustain emergent and enlarged local (gauge) and
global symmetries. We provide numerical evidence supporting this prediction. We
also find that the physical (gauge-neutral) spectral function in the OSM phase
comprises four fermion pockets, which smoothly evolve to a 'large' Fermi surface
upon approach to a Fermi liquid phase. The reconstruction of the Fermi surface
does not involve any form of translational symmetry breaking, in violation of the
Luttinger sum rule. |