Physics Colloquium: Rufus Boyack, Dartmouth University

A universal theory of incoherent metals Numerous unconventional superconductors such as cuprates, heavy-fermions, and twisted-bilayer graphene exhibit incoherent metallic transport (where the particles are short lived) above the superconducting critical temperature. One of the most striking results of these quantum materials is a linear-in-temperature resistivity at low temperatures, which cannot be described with conventional Fermi-liquid theory and has presented a significant theoretical challenge. In this talk I will discuss how the two-dimensional Yukawa-Sachdev-Ye-Kitaev model of fermions with spatially random coupling to quantum-critical bosons can provide the essential features to explain aspects of incoherent metals. One of the novel results of this microscopic model is that for highly incoherent metals the conventional Drude formula for conductivity is not applicable, and instead a non-Boltzmann transport formula between resistivity and particle lifetime is present. I will also show how highly incoherent metals violate the famous Mott-Ioffe-Regel resistivity bound and Kovtun-Son-Starinets shear viscosity to entropy density bound. This work presents the first step to solving a longstanding problem in condensed matter physics.