Twisting two graphene monolayers creates a moiré superlattice that hosts diverse exotic phases [1]—such as superconductivity, correlated insulators, nematic order, Chern insulators, magnetic polarization, and strange-metal behavior. These arise from strong band reconstruction caused by interlayer tunneling and twist. At the “magic” angle (~1°), the moiré bands flatten, amplifying Coulomb interactions and enabling many interaction-driven quantum phases [2]. Moiré superlattices have also been realized in other 2D materials, including twisted MoTe₂, WSe₂, and multilayer graphene aligned with hexagonal boron nitride. Recent experiments have, for the first time, observed fractional Chern insulating phases in twisted MoTe₂ [3] and rhombohedral pentalayer graphene [4]. These remarkable states, theoretically predicted in the early 20LFs, represent fractional quantum Hall phases that emerge without an external magnetic field. In this talk, I will first give a broad introduction to moiré materials, then discuss two topics: the predicted Chern mosaic in trilayer graphene [5] and the physical origin of a fictitious magnetic field in moiré fractional Chern insulators [6]. [1] E. Y. Andrei, A. H. MacDonald, Nature Materials 19, 1265 (2020) [2] Cao et al., Nature 556, 80 (2018) [3] Kang, Shen, Qiu, Zeng, Xia, Watanabe, Taniguchi, Shan, and Mak. Nature 628, 522–526 (2024) [4] Lu, Han, Yao, Reddy, Yang, Seo, Watanabe, Taniguchi, Fu and Long, Nature (2023) [5] D. Guerci, Y. Mao, C. Mora, PRR 6, L022025 (2024) [6] K. Kolář, K. Yang, F. von Oppen, C. Mora, PRB 1LF, 115114 (2024)

Nanographenes synthesized by bottom-up chemistry are tunable emitters with promises in optoelectronic, biosensing, and quantum technologies [1-2]. Recent investigations on the intrinsic properties of these nanographenes classify them as stable and bright single photon sources at room temperature [3-6]. The next step towards using nanographenes as quantum emitters is to reach lifetime-limited linewidth. When embedded in a polystyrene matrix, the spectral linewidth is reduced to ~ two meV at low temperature [6]. Despite this reduction, the linewidth is still a few orders of magnitude higher than the radiative limit, estimated to be a few μeV [7]. Inspired by pioneer works on small organic molecules [8], we designed a new guest/host system to decouple as much as possible the nanographene from its local environment [9]. In the first part of this presentation, we will show our recent results on the low-temperature spectroscopy of new nanographenes embedded in a new molecular crystal host [9]. In the same vein, we will show preliminary results on the spectroscopy of nanographenes deposited on the surface of h-BN. We will show that nanographene-hBN interaction can modify a lot the optical response of our quantum emitter [LF]. Finally, some perspectives on using nanographenes to build arrays of entangled emitters will be presented. References [1] Lavie, Julien, et al. "Bottom‐Up Synthesis, Dispersion and Properties of Rectangular‐Shaped Graphene Quantum Dots." Helvetica Chimica Acta LF6.6 (2023): e202300034. [2] X. Yan, X. Cui, and L.-s. Li, J. Am. Chem. Soc. CR2, 5944 (20LF) [3] Levy-Falk, Hugo, et al. "Investigation of Rod‐shaped Single Graphene Quantum Dot." physica status solidi (b) (2023). [4] S. Zhao et al, Nature Communications, 9, 3470 (2018) [5] T. Liu et al, Nanoscale, 14, 3826 – 3833 (2022) [6] T. Liu et al, Journal of Chemical Physics 156, LF4302 (2022) [7] D. Medina-Lopez et al, Nature Communications 14, 4728 (2023) [8] WP. Ambrose et al J. Chem. Phys. 95 (LF), 7150–7163 (1991) [9] Huynh Thanh Trung et al, in preparation [LF] S. Sarkar et al, in preparation