When the Coulomb repulsion between itinerant electrons dominates over their kinetic energy, the electrons in solid state materials start to develop strong correlations. Recently, moire superlattices of transition metal dichalcogenides (TMDs) have emerged as an exciting experimental platform for explorations of the resulting strongly correlated phenomena. In addition to in-situ electrical control over the electron density, these structures host tightly-bound excitons that can serve as optical charge and spin sensors of the correlated electron system.
In the first part of this talk, I will describe our low-temperature experiments on optical probing of magnetic properties of the electrons in a frustrated triangular moire superlattice hosted by MoSe2/WS2 bilayer in the vicinity of Mott-insulator state. In particular, I will show that when such a Mott state becomes electron-doped, the system exhibits unusual ferromagnetism that is driven not by Coulomb exchange interactions, but arises due to minimization of kinetic energy of itinerant electrons [1]. This observation, along with our DMRG calculations, provide direct evidence for the Nagaoka ferromagnetism in an extended two-dimensional system.
In the second part of my talk, I will demonstrate our realization of electrically-defined quantum dots (QDs) for excitons in TMD monolayers [2]. Through precise design of gate electrodes, we dynamically modulate the in-plane electric fields in our device, enabling us to confine the neutral excitons to a nanometer-sized region via the dc Stark effect. This holds a promise for implementing local optical sensors of electronic states.
[1] L. Ciorciaro, T. Smolenski, I. Morera, N. Kiper, S. Hiestand, M. Kroner, Y. Zhang, K. Watanabe, T. Taniguchi, E. Demler, A. Imamoglu, Kinetic Magnetism in Triangular Moire Materials. Nature 623, 509 (2023)
[2] D. Thureja, E. Yazici, T. Smolenski, M. Kroner, D. J. Norris, A. Imamoglu, Electrically defined quantum dots for bosonic excitons. arXiv:2402.19278 (2024)