Correlated Gapless Quantum Matter

Coordinators: Ribhu Kaul, Zhu-Xi Luo, Aavishkar Patel, Alex Thomson and Cenke Xu

Scientific Advisors: Erez Berg, Sung-Sik Lee, Subir Sachdev, and Senthil Todadri

Quantum many body systems which have excitations at arbitrarily low energies are ubiquitous across energy scales and of interest to both the condensed matter and high energy physics communities. In the most interesting cases the excitations are not described by perturbative corrections to simple theories of free particles. Correlated gapless quantum matter represent a very broad class of physical problems and include both stable phases and quantum critical points. The subjects currently under study include gapless quantum spin liquids, non-Fermi liquids and strange metals, interaction driven metal-insulator transitions, and unconventional quantum phase transitions.

The development of new analytical and numerical methods over the last decade has enabled an explosion of progress on these subjects. Examples include the proposal of a series of dualities between 2+1d quantum critical points (conformal field theories) that do not require supersymmetry; the discovery of soluble, many-body models for non-Fermi liquids and matter without quasiparticles at finite density, such as the Sachdev-Ye-Kitaev model; the development of new non-perturbative techniques for strongly interacting field theories, such as the conformal bootstrap; the understanding of new constraints imposed by anomalies on gapless states; and a series of numerical works on quantum phase transitions that lie beyond Landau's paradigm and that involve itinerant fermions.

Simultaneously, experiments on a wide range of systems such as quantum spin liquid Mott insulators, Moiré van der Waals materials, heavy fermion metals and the normal state of cuprate superconductors have provided puzzling observations of correlated gapless quantum matter. This program aims to serve as a platform for the confluence of theory, numerical simulations, and experiment that can challenge our current understanding and inspire future progress. Focused on the new frontiers of gapless states of matter, the program will connect condensed matter and high energy physics theorists to one another and incorporate the latest developments in condensed matter experimental research.