Excitonic insulator states in molecular functionalized atomically-thin semiconductors

Abstract

The excitonic insulator is an elusive electronic phase exhibiting a correlated excitonic ground state. Materials with such a phase are expected to have intriguing properties such as excitonic high-temperature superconductivity. However, compelling evidence on the experimental realization is still missing. Here, we theoretically propose hybrids of two-dimensional semiconductors functionalized by organic molecules as prototypes of excitonic insulators, with the exemplary candidate WS2-F6TCNNQ. This material system exhibits an excitonic insulating phase at room temperature with a ground state formed by a condensate of interlayer excitons. To address an experimentally relevant situation, we calculate the corresponding phase diagram for the important parameters: temperature, gap energy, and dielectric environment. Further, to guide future experimental detection, we show how to optically characterize the different electronic phases via far-infrared to terahertz (THz) spectroscopy.

Impact of dark excitons on Förster-type resonant energy transfer between dye molecules and atomically thin semiconductors

“…The large oscillator strength of optically bright excitons makes TMDC monolayers ideal resonant substrates for energetically tunable molecules, but also for quantum dots [24][25][26][27], NV centers [28] and plasmonic structures [29][30][31][32]. On the other hand, it is known that optically dark, momentum forbidden TMDC excitons contribute strongly to the excitonic dynamics [33][34][35][36][37][38][39] and may become visible if the translational invariance is broken by a zero-dimensional molecular emitter.…”