Bright Dipolar Excitons with Valley-Locked and Polarization-Tunable Orientations in Monolayer Ti2SiCO2.

Abstract

While monolayer systems hosting bright dipolar excitons with tunable dipole orientations hold great promise for applications in optoelectronic devices and quantum technologies, the identification and realization of such systems with unique properties remain elusive. Here, using first-principles GW Bethe-Salpeter equation calculations and symmetry analysis, we demonstrate that the Ti₂SiCO₂ monolayer hosts out-of-plane bright dipolar excitons with valley-locked and polarization-tunable orientations. These dipolar excitons exhibit valley-selective linear dichroism, high oscillator strengths, and dipole orientations that can be controlled via light polarization. Additionally, a pronounced linear quantum-confined Stark effect is found by using an effective tight-binding model. With long lifetimes, large radii, and substantial binding energies, the dipolar excitons in the Ti₂SiCO₂ monolayer make it possible to achieve high-temperature excitonic Bose-Einstein condensation and superfluidity, with transition temperatures of 104.3 and 26.1 K, respectively. Our findings establish the Ti₂SiCO₂ monolayer as a promising platform for exploring tunable correlated excitonic phenomena and designing dissipationless quantum devices.