The effect of the electron-phonon coupling on the effective thermal conductivity of metal-nonmetal multilayers

The metal-nonmetal interface plays a critical role in modern electronic and energy conversion devices. For example, metal-nonmetal multilayered structures have recently been proposed as promising materials for solid-state thermionic devices, which could potentially achieve an efficiency that might not be feasible for metals or semiconductors alone. In this work, the effective thermal conductivity of a metal-nonmetal multilayered system (superlattices) is studied using the two-temperature model of heat conduction. By defining the total interfacial thermal resistance, which strongly depends on the electron-phonon coupling factor, it is shown that the thermal conductivity of the system has a simple interpretation as the sum of thermal resistances in series. The role of the electron-phonon coupling and the phonon-phonon interfacial thermal resistance on the total interfacial thermal resistance is discussed. The derived analytical expressions show that the effective thermal conductivity of the multilayered structure is, remarkably, determined by the ratio between the thickness of the metal layers and their intrinsic electron-phonon coupling length. It is demonstrated that the effective thermal conductivity of the metal-nonmetal system can be smaller, equal to, or larger than the thermal conductivity of the nonmetal layer, depending on the length of the metal layer.