Two-dimensional (2D) and layered materials with specific crystal structures can yield a wide range of quantum phases and electronic properties. For instance, 2D systems with a kagome crystal structure – where atoms or molecules are arranged in corner-sharing equilateral triangles – can host electronic wavefunctions that interfere destructively, resulting in highly localised electronic states and strong electron-electron Coulomb interactions. These interactions can lead to a vast range of many-body quantum phenomena (e.g., Mott metal-insulator transitions, correlation-induced magnetism, quantum spin liquids, unconventional superconductivity), tunable via the occupancy of the system’s electronic states (i.e., via the system’s chemical potential).
Another example of tuneable electronic properties is given by 2D materials interacting with light, including optical control of electronic band structure and topology [1].
My talk will be divided in two parts. In the first part, I will present results on a 2D metal-organic framework (MOF) consisting of flat aromatic molecules arranged in a kagome structure via coordination with copper atoms. Scanning tunneling microscopy (STM) and spectroscopy measurements reveal that, when adsorbed on a weakly interacting metal surface, this 2D kagome MOF hosts local magnetic moments which arise from strong electron-electron Coulomb interactions given by the kagome geometry [2]. On an atomically thin insulator, the same 2D kagome MOF exhibits a ~200 meV electronic energy gap which is consistent with a Mott insulating phase [3]. By exploiting local work function variations of the substrate and the electrostatic potential applied with the STM probe, we are able to locally tune the occupancy of electronic states and induce Mott metal-insulator transitions in this MOF. These findinds open the door to nanoelectronics and spintronics technologies based on 2D MOFs and on electrostatic control of many-body quantum phases therein.
In the second part of my talk, I will discuss steps towards control of band structure and electronic topology of graphene with optical fields. I will present results on electronic properties of graphene probed with THz waveforms [4], and on changes of these electronic properties resulting from irradatiation with visible and infrared light.

[1] T. Oka et al. Annu. Rev. Condens. Matter Phys. 10, 387 (2019)
[2] D. Kumar et al. Adv. Funct. Mater., 31, 2106474 (2021)
[3] B. Lowe et al. Nature Commun. 15, 3559 (2024)
[4] T.-P. Nguyen et al. arXiv:2310.06180 (2023)