2023/01/15 by Aidan Delgado, Carolin Dusold, Delgado, Aidan +9 · 2 citations
Physics and Astronomy · #Advanced Condensed Matter Physics #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Quantum and electron transport phenomena #Quantum, superfluid, helium dynamics #Strongly Correlated Electrons (cond-mat.str-el)
paper · pdf · doi:10.48550/arxiv.2301.06171
openalex publication_date 2023/01/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Electron-hole pair excitations in semiconductors have been predicted to be able to give rise to a highly correlated many-body ground state, the excitonic insulator (EI). Under appropriate conditions below a critical temperature (Tc), strongly bound electron-hole pairs spontaneously form and undergo a phase transition from a normal band insulator into an exciton condensate, transforming the parent material into a novel correlated insulator. Despite recent advances in spectroscopic tools, clear direct experimental evidence for the EI state has been elusive and is often obfuscated by accompanying electronic effects. Here we present the reticular bottom-up synthesis of a Kagome lattice of [4]triangulene, a two-dimensional (2D) covalent organic framework (COF) imbued with a deliberate excitonic instability excitons with binding energies larger than the bandgap arising from a pair of flat bands (FBs). Theoretical analyses based on first-principles calculations and scanning tunnelling spectroscopy (STS) reveal quasiparticle spectral signatures mixing valence (VB) and conduction (CB) characteristics of the FBs along with a non-trivial semiconducting gap that can only be explained by invoking many-body theory. Our findings spectroscopically corroborate the nature of a FB induced exciton insulator ground state and provide a robust yet highly tuneable platform for the exploration of correlated quasi boson physics in quantum materials.