Heat can flow backward from cold to hot regions, rather than diffusing randomly, in certain materials like graphite and graphene

https://www.eurekalert.org/news-releases/1115922

"heat carried by phonons (vibrations), but these phonons can flow collectively like water in a pipe... injecting heat into specific points can create vortices on flow's sides, pushing heat back from cold regions toward hot ones, making thermal resistance across device negative... prevent overheating in smartphones, batteries, computers, more effectively than traditional cooling... can be applied to other systems such as electrons (in plasmonics)/ magnons (magnetic storage)... future: apply at higher temperatures than 70°K"