Going beyond Landauer scattering theory to describe spatially resolved nonlocal heating and cooling in quantum thermoelectrics

Spatially resolved heating and cooling in nanostructures is nowadays measured with various nanoscale thermometry techniques, including scanning thermometry. Yet, the most commonly used theory of nanoscale heating and thermoelectricity, Landauer scattering theory, is not appropriate to model such measurements. Hence, we analyze a minimal model of spatially resolved heat transfer between electrons and phonons in simple thermoelectric nanostructures. This combines Landauer scattering formalism with a Boltzmann equation for transport, revealing the nonlocality of Joule heating and Peltier cooling induced by a scatterer in a nanowire. The corresponding heating or cooling of the phonons is caused by the voltage drop at the scatterer, but is often maximal at a certain distance from the scatterer. This distance is of the order of the electron-phonon scattering length. Scanning thermal microscopy, such as SQUID-on-tip thermometers, should detect this nonlocality as phonon hot spots and cold spots, spatially separated from the scatterer. We provide physical arguments explaining the thermoelectric response of the combined system of wire and scatterer and, in particular, why the resulting heating and cooling is sometimes the opposite to that predicted by the standard Landauer scattering theory.