Thermal spin photonics in the near-field of nonreciprocal media

Abstract

The interplay of spin angular momentum and thermal radiation is a frontier area of interest to nanophotonics as well as topological physics. Here, we show that a thick planar slab of a nonreciprocal material, despite being at thermal equilibrium with its environment, can exhibit nonzero photon spin angular momentum and nonzero radiative heat flux in its vicinity. We identify them as the persistent thermal photon spin and the persistent planar heat current respectively. With a practical example system, we reveal that the fundamental origin of these phenomena is connected to the spinmomentum locking of thermally excited evanescent waves. We also discover spin magnetic moment of surface polaritons that further clarifies these features. We then propose an imaging experiment based on Brownian motion that allows one to witness these surprising features by directly looking at them using a lab microscope. We further demonstrate the universal behavior of these near-field thermal radiation phenomena through a comprehensive analysis of gyroelectric, gyromagnetic and magneto-electric nonreciprocal materials. Together, these results expose a surprisingly little explored research area of thermal spin photonics with prospects for new avenues related to non-Hermitian topological photonics and radiative heat transport.

Near-field radiative heat transfer in many-body systems

“…In other words, no heat is finally emitted. Similar conclusions have been made for the thermal radiation field of the nonreciprocal surface modes on planar interfaces (Khandekar and Jacob, 2019a;Silveirinha, 2017).…”

“…Using these definitions together with FE the persistent angular momentum close to the walls of a cavity was first evaluated and discussed in (Silveirinha, 2017) and the angular momentum and spin for a thermally emitting nanoparticle by (Ott et al, 2018). A more detailed study of the angular momentum and spin close to a planar interface has been published recently (Khandekar and Jacob, 2019a).…”

“…From (Ott et al, 2018) for instance. More recently, circularly polarized thermal emitters based on chiral meta-surfaces (Dyakov et al, 2018) and nano-antennas (Khandekar and Jacob, 2019b) have been proposed.…”

“…Recently, a setup has been proposed in Ref. (Khandekar and Jacob, 2019a) which might be able to access it in the vicinity of a magneto-optical planar sample.…”

Chiral Absorbers Based on Polarization Conversion and Excitation of Magnetic Polaritons

“…Ouyang et al [9] proposed a plasmonic metasurface consisting of a three-layer meta-dielectric-metal structure, which can achieve a maximum CD of 0.7. Khandekar and Jacob [22] proposed a strategy for realizing chiral thermal emission with coupled anisotropic antennas at thermal non equilibrium, from which the thermal photon spin [23,24] was controlled by the nonequilibrium temperature of the antennas. However, all of these structures demand complex fabrication processes.…”