Non-equilibrium Green's function formalism for radiative heat transfer

Area of Science:

• Physics
• Materials Science
• Quantum Mechanics

Background:

• Nanoscale radiative heat transfer (RHT) traditionally uses fluctuational electrodynamics (FE), which is limited to local thermal equilibrium.
• Active devices and driven materials present non-equilibrium conditions where FE breaks down.

Purpose of the Study:

• Introduce the non-equilibrium Green's function (NEGF) formalism for studying RHT beyond classical limits.
• Demonstrate NEGF's ability to unify various energy transport mechanisms.
• Highlight NEGF's potential for quantum design and active control of thermal energy.

Main Methods:

• Theoretical framework based on quantum many-body theory.
• Application of NEGF to describe energy transport by photons, electrons, and phonons.
• Comparison of NEGF results with FE in the local equilibrium limit.

Main Results:

• NEGF provides quantum-accurate equilibrium RHT, incorporating non-local and finite-size effects.
• Revealed synergistic heat transfer across sub-nanometer gaps involving radiation, electron tunneling, and phonon conduction.
• Enabled quantum design of materials for tailored thermal properties.
• Described active control of heat flow in driven systems, including isothermal transfer and heat pumping.

Conclusions:

• NEGF formalism offers a versatile framework for nanoscale RHT under non-equilibrium conditions.
• NEGF facilitates the quantum design of materials and metamaterials for advanced thermal applications.
• This approach opens new frontiers in thermal management, energy conversion, and thermal information processing.