When two solids at different temperatures are separated by a vacuum gap they relax toward their equilibrium state by exchanging heat either by radiation or by phonon or electron tunneling, depending on their separation distance and on the nature of materials. The interplay between this exchange of energy and its spreading through each solid entirely drives the relaxation dynamics. Here we highlight a significant slowing-down of this process in the extreme near-field regime at distances where the heat flux exchanged between the two solids is comparable or even dominates over the flux carried by conduction inside each solid. This mechanism, leading to a strong effective increase in the system thermal inertia, should play an important role in the temporal evolution of the thermal state of interacting solid systems at nanometric and subnanometric scales.

• Received 28 June 2021
• Revised 30 August 2021
• Accepted 13 September 2021

DOI:https://doi.org/10.1103/PhysRevB.104.L100305