Shining light on moiré matter: From atomic structures to optical excitations

Placing two identical transparent patterned sheets on top of each other and rotating one relative to the other creates a striking moiré pattern. Since 2018, physicists have recreated this effect at the atomic scale using two-dimensional materials such as graphene and transition-metal dichalcogenides. The resulting moiré materials show a wide range of intriguing electronic, vibrational, and optical properties, from superconductivity to long-lived electronic excitations—all easily tunable by changing the twist angle, doping, and device design. A major challenge in modelling these materials is their large moiré unit cells, which can contain thousands of atoms. Standard first-principles methods are often not feasible for studying optical properties, such as how moiré materials absorb light. In this talk, I will present our recently developed theoretical methods for overcoming this challenge. I will introduce an efficient many-body perturbation theory framework for calculating optical excitations using a localized Wannier-function basis [1,2]. This approach allowed us to resolve a seven-year-old puzzle about the nature of intralayer excitons in a moiré material with meV accuracy [3]. We also develop a transfer-matrix formalism to capture Coulomb interactions in arbitrarily twisted multilayer 2D materials. Using this approach, we show that large atomic rearrangements can trap dipolar [4] and quadrupolar [5] excitons in moiré materials. We further show that these dipolar and quadrupolar excitons can generate quantum phonon states, including coherent and squeezed phonons [6]. Our work opens new avenues for understanding and designing electronic excitations for next-generation optoelectronics and quantum technologies.

References:
1. I. Maity, A. Mostofi, J. Lischner, NPJ 2D Materials & Applications 9, 20 (2025).
2. I. Maity, P. Chodyra, J. A. Dawson, J. Lischner, A Mostofi, Invited article to be submitted (2026).
3. I. Maity, J. Lischner, A. Mostofi, Á. Rubio, Nano Letters 26, 1349-1356 (2026).
4. Z. Lian*, Y. Meng*, L. Ma*, I. Maity* et al., Nature Physics 20, 34-39 (2024).
5. I. Maity, A. Mostofi, Á. Rubio, J. Lischner, Revision at Nature Communications (2026).
6. I. Maity, A. Mostofi, J. Lischner, Á. Rubio, Manuscript in preparation (2026).