Thermal switches based on mechanical actuation or fluids flows are essential components in magnetocaloric and electrocaloric refrigeration cycles and other existing technologies.  Efficient solid-state thermal switches can not only enhance the cycling reproducibility of these refrigeration cycles but also enable high-performance phase change memories, thermal camouflage, and other emerging electronic and energy conversion devices.  Existing approaches to tunable thermal transport in solids rely either on structural phase transformations or on modification of the scattering rates of energy carriers, typically either phonons or electrons. The switching ratios and speeds of these approaches are insufficient to realize solid-state thermal switches, rheostats, regulators, or transistors that are as effective as their mechanical or fluid counterparts.

This multidisciplinary research team project investigates new routes to achieve rapid, large, and reversible electronic switching of heat transport in solids and outlines a research program intended to lay the groundwork for practical devices. Building on recent discoveries of topological and collective electronic states, three related approaches are identified to achieve extraordinary electronic switching of thermal transport in bulk crystals, along thin films, and across interfaces. These approaches are based on the chiral anomaly in Weyl semimetals, excitonic heat transport, and resonant Coulomb energy transfer between two-level systems.

This MURI program will investigate these three electronic thermal switching mechanisms as well as approaches to suppress the parasitic phonon thermal transport. Each of the approaches not only leverages cutting-edge research in condensed matter physics to create thermal switches, but also pushes the frontiers of research in condensed matter physics, offering the potential for scientific breakthroughs involving topologically controlled correlated electron and spin physics. In addition, this project identifies four different devices and systems where thermal switches could play critical, enabling roles. Successful realization of high-performance solid-state thermal switching devices would directly impact a range of technologies.