On the afternoon of April 28, the physics topic of "HUST-NUS academic lecture series" was successfully held. Prof. Jiansheng Wang, from Department of Physics, NUS, gave a lecture titled with"Energy, momentum, and angular momentum transfers mediated by photons". More than 100 scientific researches from home and abroad participated online.

Prof. Wang said that black-body radiation and Casimir force are well-known. Black-body radiation is energy transfer, while Casimir force between metal plates is momentum transfer. Here, we consider N objects in vacuum each locally may in thermal equilibrium but globally in nonequilibrium steady state. Transport of energy, momentum, or angular momentum is then possible mediated by the electromagnetic fields. It is useful to also consider an extra N+1 “object” which is the “bath-at-infinity” for conservation laws. Very general formulas of Meir-Wingreen type are derived based on the nonequilibrium Green’s functions (NEGF) for the photon field and the Keldysh formalism. The materials properties are represented by self-energies. We illustrate the usefulness of the formulas and present some results of calculations, such as the angular momentum emission by a benzene ring driven by electric current, energy and angular momentum emission from a Haldane model of electrons, and also energy, momentum, and angular momentum emissions from graphene edges in nonequilibrium states.

Biography of the speaker:

Jian-Sheng Wang, APS Fellow (2005), Professor at the Department of Physics, National University of Singapore. He received his Bachelor degree from Jilin University (China) in 1982, and PhD degree from Carnegie Mellon University (USA) in 1987. He has been working at the Department of Physics, National University of Singapore since 1993, previously acting as a Depute Head of Department of Computational Science and Department of Physics. From 2004 to 2006, he was an Adjunct Professor at the School of Physics, HUST.

Prof. Wang is well-known for his work on using Monte Carlo simulation to solve problems in statistical mechanics. The Swendsen-Wang algorithm has been written into many textbooks of statistical physics and computational physics. In 2022, his new book titled“Advanced Statistical Mechanics” was published. In the past two decades, his research interest has shifted to quantum transport in nanostructures and the development of the nonequilibrium Green’s function (NEGF) method. He has been working on thermal transport via molecular dynamics and NEGF, electron-phonon interactions, thermal Hall effect, quantum master equations in transport. Mostly recently, he focuses on the near-field radiative heat transfer, transport of angular momentum, and Casimir force.