Microscopic theory of photon-induced energy, momentum, and angular momentum transport in the nonequilibrium regime

TL;DR

This paper develops a microscopic nonequilibrium Green's function theory for photon-mediated energy, momentum, and angular momentum transfer, applicable to complex systems beyond traditional fluctuational electrodynamics.

Contribution

It introduces a unified formalism that does not rely on local thermal equilibrium or reciprocity, enabling analysis of nonreciprocal and nonequilibrium photon transport in arbitrary systems.

Findings

Graphene edge energy radiation follows T^4 law with 2.058% emissivity.

Nonzero force and torque observed in nonequilibrium graphene transport.

Method applicable to large, complex systems beyond conventional theories.

Abstract

We set up a general microscopic theory for the transfer of energy, momentum, and angular momentum mediated by photons. Using the nonequilibrium Green's function method, we propose a unified Meir-Wingreen formalism for the energy emitted, force experienced, and torque experienced by the objects due to the fluctuating electromagnetic field. Our theory does not require the local thermal equilibrium that is the central assumption of the conventional theory of fluctuational electrodynamics (FE). The obtained formulas are valid for arbitrary objects as well as the environment without the requirement of reciprocity. To show the capability of our microscopic theory, we apply the general formulas to transport problems of graphene edges in both equilibrium and nonequilibrium situations. We show the local equilibrium energy radiation of graphene obeys the well-known $T^4$ law with a converged theoretical emissivity of 2.058$\%$. In the ballistic nonequilibrium situation driven by chemical potential biases, we observe nonzero results for force and torque from the graphene edges, which go beyond the predictive ability of the FE theory. Our method is general and efficient for large systems, which paves the way for studying more complex transport phenomena in the nonequilibrium regime.