Quantum chaos on a critical Fermi surface

Significance All high-temperature superconductors exhibit a remarkable “strange metal” state above their critical temperatures. A theory of the strange metal is a prerequisite for a deeper understanding of high-temperature superconductivity, but the ubiquitous quasiparticle theory of normal metals cannot be extended to the strange metal. Instead, strange metals exhibit many-body chaos over the shortest possible time allowed by quantum theory. We characterize the quantum chaos in a model of fermions at nonzero density coupled to an emergent gauge field. We find a universal relationship between the chaos parameters and the experimentally measurable thermal diffusivity. Our results establish a connection between quantum dephasing and energy transport in states of quantum matter without quasiparticles.