Fractons

TL;DR

This review explores the unique properties, theoretical frameworks, and connections of fracton phases of quantum matter, highlighting their restricted excitations, relation to gauge theories, and potential links to gravity and elasticity.

Contribution

It provides a comprehensive overview of both gapped and gapless fracton phases, introducing tensor gauge theory as a key framework and connecting fractons to various physical theories.

Findings

Fracton phases exhibit excitations with restricted mobility.

Tensor gauge theory effectively describes fracton phenomena.

Connections between fractons, elasticity, and gravity are established.

Abstract

We review what is known about fracton phases of quantum matter. Fracton phases are characterized by excitations that exhibit restricted mobility, being either immobile under local Hamiltonian dynamics, or mobile only in certain directions. They constitute a new class of quantum state of matter, which does not wholly fit into any of the existing paradigms, but which connects to areas including glassy quantum dynamics, topological order, spin liquids, elasticity theory, quantum information theory, and gravity. We begin by discussing gapped fracton phases, which may be described using exactly solvable lattice spin models. We introduce the basic phenomena, and discuss the geometric and topological response of fracton phases. We also discuss connections to generalized gauge theories, and explain how gapped fracton phases may be obtained from more familiar theories. We then introduce the framework of tensor gauge theory, which provides a powerful complementary perspective on fracton phases. We discuss how tensor gauge theory encodes the fracton phenomenon, and how it allows us to access gapless fracton phases. We discuss the basic properties of gapless fracton phases, and their connections to elasticity theory and gravity. We also discuss what is known about the dynamics and thermodynamics of fractons at non-zero density, before concluding with a brief survey of some open problems.