We discuss a new class of quantum phase transitions—deconfined Mott transition (DMT)—that describe a continuous transition between a Fermi liquid metal with a generic electronic Fermi surface and an electrical insulator without Fermi surfaces of emergent neutral excitations. We construct a unified $U\left(2\right)$ gauge theory to describe a variety of metallic and insulating phases, which include Fermi liquids, fractionalized Fermi liquids (FL*), conventional insulators, and quantum spin liquids, as well as the quantum phase transitions between them. Using the DMT as a basic building block, we propose a distinct quantum phase transition—deconfined metal-metal transition (${\mathrm{DM}}^2\mathrm{T}$)—that describes a continuous transition between two metallic phases, accompanied by a jump in the size of their electronic Fermi surfaces (also dubbed a ‘Fermi transition'). We study these new classes of deconfined metallic quantum critical points using a renormalization group framework at the leading nontrivial order in a controlled expansion and comment on the various interesting scenarios that can emerge going beyond this leading order calculation. We also study a $U\left(1\right)\times U\left(1\right)$ gauge theory that shares a number of similarities with the $U\left(2\right)$ gauge theory and sheds important light on many phenomena related to DMT, ${\mathrm{DM}}^2\mathrm{T}$, and quantum spin liquids.

• Received 19 February 2020
• Accepted 27 May 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.023344

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Published by the American Physical Society