Cryogenic Characteristics of Graphene Composites -- Evolution from Thermal Conductors to Thermal Insulators

TL;DR

This study explores how graphene composites can act as either thermal conductors or insulators at cryogenic temperatures, depending on filler loading and temperature, with implications for quantum computing and cryogenic electronics.

Contribution

It introduces a physical model explaining the temperature-dependent thermal behavior of graphene composites, highlighting their dual role as conductors and insulators at cryogenic temperatures.

Findings

Thermal conductivity of graphene composites varies with temperature and filler loading.

A cross-over temperature determines whether composites conduct or insulate heat.

Graphene fillers can serve as phonon scattering centers or heat conduits.

Abstract

The development of cryogenic semiconductor electronics and superconducting quantum computing requires composite materials that can provide both thermal conduction and thermal insulation. We demonstrated that at cryogenic temperatures, the thermal conductivity of graphene composites can be both higher and lower than that of the reference pristine epoxy, depending on the graphene filler loading and temperature. There exists a well-defined cross-over temperature - above it, the thermal conductivity of composites increases with the addition of graphene; below it, the thermal conductivity decreases with the addition of graphene. The counter-intuitive trend was explained by the specificity of heat conduction at low temperatures: graphene fillers can serve as, both, the scattering centers for phonons in the matrix material and as the conduits of heat. We offer a physical model that explains the experimental trends by the increasing effect of the thermal boundary resistance at cryogenic temperatures and the anomalous thermal percolation threshold, which becomes temperature dependent. The obtained results suggest the possibility of using graphene composites for, both, removing the heat and thermally insulating components at cryogenic temperatures - a capability important for quantum computing and cryogenically cooled conventional electronics.