Condensed Matter Seminar - "Unified theories of transport in solids: from crystals to glasses, and from diffusion to viscous hydrodynamics"

The relationship between atomic structure and macroscopic physical properties of solids has intrigued scientists since the early days of quantum theory, and underpins many technologies. We will explore the atomistic mechanisms that govern the formation of defects and disorder in solids, leveraging ab-initio simulations and machine learning1 to quantitatively predict how they affect properties ranging from (alter)magnetism to transport of heat, charge, and light. To describe transport, we start from the Wigner transport equation, which unifies and extends the established theories for vibrational thermal transport in crystals and glasses, and extend it to describe vibrations coupled with electrons or photons. Finally, we will discuss how extrinsic, device-induced effects at the nano- and micro-scale can be captured by coarse-graining the microscopic equations into mesoscopic models that transcend ordinary diffusion. Overall, this framework rationalizes observations of hydrodynamic heat transport and opens opportunities to induce, control, and ultimately exploit fluid-like thermoelectric transport6 in electronic or neuromorphic technologies.