Fractionalized Fermi Liquids
In spatial dimensions $d\ensuremath{\ge}2$, Kondo lattice models of conduction and local moment electrons can exhibit a fractionalized, nonmagnetic state (${\mathrm{F}\mathrm{L}}^{*}$) with a Fermi surface of sharp electronlike quasiparticles, enclosing a volume quantized by $({\ensuremath{\rho}}_{a}\ensuremath{-}1)(\mathrm{m}\mathrm{o}\mathrm{d}\text{ }2)$, with ${\ensuremath{\rho}}_{a}$ the mean number of all electrons per unit cell of the ground state. Such states have fractionalized excitations linked to the deconfined phase of a gauge theory. Confinement leads to a conventional Fermi liquid state, with a Fermi volume quantized by ${\ensuremath{\rho}}_{a}(\mathrm{m}\mathrm{o}\mathrm{d}\text{ }2)$, and an intermediate superconducting state for the ${Z}_{2}$ gauge case. The ${\mathrm{F}\mathrm{L}}^{*}$ state permits a second order metamagnetic transition in an applied magnetic field.