Electron cooling in graphene enhanced by plasmon-hydron resonance

TL;DR

This study demonstrates that water uniquely accelerates electron cooling in graphene through a resonance between surface plasmons and water charge fluctuations, revealing a quantum mechanism for solid-liquid heat transfer.

Contribution

It provides the first experimental evidence of resonance-mediated solid-liquid energy transfer involving collective modes, advancing understanding of quantum friction and thermal conductance.

Findings

Water enhances graphene electron cooling via plasmon-hydron resonance.

Resonance with water libration modes facilitates efficient energy transfer.

Water-graphene interface exhibits large thermal boundary conductance.

Abstract

Evidence is accumulating for the crucial role of a solid's free electrons in the dynamics of solid-liquid interfaces. Liquids induce electronic polarization and drive electric currents as they flow; electronic excitations, in turn, participate in hydrodynamic friction. Yet, the underlying solid-liquid interactions have been lacking a direct experimental probe. Here, we study the energy transfer across liquid-graphene interfaces using ultrafast spectroscopy. The graphene electrons are heated up quasi-instantaneously by a visible excitation pulse, and the time evolution of the electronic temperature is then monitored with a terahertz pulse. We observe that water accelerates the cooling of the graphene electrons, whereas other polar liquids leave the cooling dynamics largely unaffected. A quantum theory of solid-liquid heat transfer accounts for the water-specific cooling enhancement through a resonance between the graphene surface plasmon mode and the so-called hydrons -- water charge fluctuations --, particularly the water libration modes, that allows for efficient energy transfer. Our results provide direct experimental evidence of a solid-liquid interaction mediated by collective modes and support the theoretically proposed mechanism for quantum friction. They further reveal a particularly large thermal boundary conductance for the water-graphene interface and suggest strategies for enhancing the thermal conductivity in graphene-based nanostructures.