Twist-tailoring Coulomb correlations in van der Waals homobilayers
Philipp Merkl, Fabian Mooshammer, Samuel Brem, Anna Girnghuber, Kai-Qiang Lin, Leonard Weigl, Marlene Liebich, Chaw‐Keong Yong, Roland Gillen, Janina Maultzsch, John M. Lupton, Ermin Malić, R. Huber
Abstract
Abstract The recent discovery of artificial phase transitions induced by stacking monolayer materials at magic twist angles represents a paradigm shift for solid state physics. Twist-induced changes of the single-particle band structure have been studied extensively, yet a precise understanding of the underlying Coulomb correlations has remained challenging. Here we reveal in experiment and theory, how the twist angle alone affects the Coulomb-induced internal structure and mutual interactions of excitons. In homobilayers of WSe 2 , we trace the internal 1 s –2 p resonance of excitons with phase-locked mid-infrared pulses as a function of the twist angle. Remarkably, the exciton binding energy is renormalized by up to a factor of two, their lifetime exhibits an enhancement by more than an order of magnitude, and the exciton-exciton interaction is widely tunable. Our work opens the possibility of tailoring quasiparticles in search of unexplored phases of matter in a broad range of van der Waals heterostructures.