Emergent Phenomena in the thermal-radiative response of vdW materials

In many nanostructured materials, the stability of sub-nanometric elementary units relies on strong covalent bonding, while the entire assembly is held together by weak van der Waals interactions. Consequently, individual building blocks maintain their intrinsic characteristics even when organised into a crystalline solid. This principle allows for the tailoring of novel material properties by controlling those of the elementary units. The bottom-up synthesis strategy for new materials has been actively pursued since the '80s, gaining significant attention with the exploration of small atomic aggregates, nanoclusters, fullerenes, nanotubes, and more [1-2].

In this context, the interest in low-dimensional materials is self-evident. On the one hand, the physics of many-body systems, limited in 2D or 1D, unveils a plethora of unusually fascinating properties. Simultaneously, the reduction of dimensionality enables gedanken experiments for testing and enhancing our understanding of physical models.

In this presentation, I will focus on the thermal-radiative response presenting a parallel study of the radiative linewidths of excitons and phonons in atomically thin layers of h-B, comparing the peculiar properties of hBN with respect to other 2D semiconductors. I will then present the emergence of some exotic phenomena, such as the possibility to observe the superradiance of optical phonons during the 2D → 3D crossover [3-5].

[1] M. S. Dresselhaus et al, Science of Fullerenes and Carbon Nanotubes: Their Properties and Applications (Academic, San Diego, 1996).

[2] P. Moriarty, Rep. Prog. Phys. 64, 297 (2001).

[3] C. Elias, et al. Flat bands and giant light-matter interaction in hexagonal boron nitride PRL 127 (13), 137401 (2021).

[4] G. Cassabois et al. Superradiance of optical phonons in two-dimensional materials Phys Rev. Research 4 (3), L032040 (2022)

[5] G. Cassabois et al Exciton and phonon radiative linewidths in monolayer boron nitride PRX 12 (1), 011057 (2022)