Unconventional bright ground-state excitons in monolayer TiI from first-principles calculations
arXiv:2512.09602 · doi:10.1038/s41699-025-00656-z
Abstract
Based on \textit{ab initio} screened configuration interaction calculations we find that TiI has a bright exciton ground state and identify two key mechanisms that lead to this unprecedented feature among transition metal dichalcogenides. First, the spin-orbit induced conduction band splitting results in optically allowed spin-alignment for electrons and holes across a significant portion of the Brillouin zone around the -valley, avoiding band crossings seen in materials like monolayer MoSe. Second, a sufficiently weak exchange interaction ensures that the bright exciton remains energetically below the dark exciton state. We further show that the bright exciton ground state is stable under various mechanical strains and that trion states (charged excitons) inherit this bright ground state. Our findings are expected to spark further investigation into related materials that bring along the two key features mentioned, as bright ground-state excitons are crucial for applications requiring fast radiative recombination.
References in corpus (26)
- Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
- Atomically thin MoS2: A new direct-gap semiconductor
- Advanced capabilities for materials modelling with Quantum ESPRESSO
- The PseudoDojo: Training and grading a 85 element optimized norm-conserving pseudopotential table
- The Computational 2D Materials Database: High-Throughput Modeling and Discovery of Atomically Thin Crystals
- Tightly bound excitons in monolayer WSe2
- Yambo: an \textit{ab initio} tool for excited state calculations
- Computational 2D Materials Database: Electronic Structure of Transition-Metal Dichalcogenides and Oxides
- Bright triplet excitons in lead halide perovskites
- Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides
- Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors
- Many-body perturbation theory calculations using the yambo code
- Large spin splitting in the conduction band of transition metal dichalcogenide monolayers
- Direct Bandgap Emission from Hexagonal Ge and SiGe Alloys
- Density functional perturbation theory for gated two-dimensional heterostructures: Theoretical developments and application to flexural phonons in graphene
- Splitting between Bright and Dark excitons in Transition Metal Dichalcogenide Monolayers
- Biaxial strain tuning of the optical properties of single-layer transition metal dichalcogenides
- Brightening of dark excitons in monolayers of semiconducting transition metal dichalcogenides
- Dark excitons in transition metal dichalcogenides
- A Room Temperature Polariton Light-Emitting Diode Based on Monolayer WS2
- Control of the Exciton Radiative Lifetime in van der Waals Heterostructures
- Gate tunable dark trions in monolayer WSe
- Localized bright luminescence of indirect excitons and trions in MoSe/WSe van der Waals heterostructure
- Ab Initio Calculations of Exciton Radiative Lifetimes in Bulk Crystals, Nanostructures and Molecules
- Neutral and charged dark excitons in monolayer WS
- Tensile strain induced brightening of momentum forbidden dark exciton in WS