Excitons de transferência de carga em bicamadas de semicondutores rotacionadas

Abstract

Two-dimensional semiconductors constitute a promising platform for engineering next-generation optoelectronic devices. In addition, van der Waals structures formed by the vertical stacking of these materials have further expanded the range of systems to be studied, since this stacking can give rise to optical, electronic, and mechanical properties that do not exist in the individual constituent materials. Furthermore, the relative rotation between layers in these structures introduces an additional degree of freedom. This rotation gives rise to a periodic pattern, called a moiré pattern, which induces spatial modulations in the valence and conduction bands along the material plane. These modulations can be viewed in the continuum model as an effective periodic potential felt by the charge carriers present in the semiconductor. The moiré exciton is a quasiparticle formed when the electron-hole interaction is strong, where the electron and hole are confined in the same region of the material. In the case where the moiré potential is comparable to the interaction potential, the exciton center-of-mass coordinates cannot be separated from the relative coordinates, and the concept of moiré exciton fails. In this work, we propose a model that allows the transition between the regime of moiré electrons and holes, in-plane spatially indirect excitons, and the regime of moiré excitons. Our results show that even in situations where the moiré potential confines electrons and holes in the same regions of the plane, the conventional models used in the literature to calculate the exciton binding energy underestimate their actual values.